System and method for testing contact quality of electrical-biosignal electrodes

ABSTRACT

One variation of a method for testing contact quality of electrical-biosignal electrodes includes: outputting a drive signal through a driven electrode, the drive signal comprising an alternating-current component oscillating at a reference frequency and a direct-current component; reading a set of sense signals from a set of sense electrodes at a first time; calculating a first combination of the set of sense signals; calculating a first direct-current value comprising a combination of the first combination and the direct-current component of the drive signal at approximately the first time; and at a second time succeeding the first time, shifting the direct-current component of the drive signal output by the driven electrode to the first direct-current value.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation application of U.S. patentapplication Ser. No. 17/875,342, filed on 27 Jul. 2022, which is acontinuation application of U.S. patent application Ser. No. 16/854,585,filed on 21 Apr. 2020, and Ser. No. 16/854,568, filed on 21 Apr. 2020,each of which is a continuation application of U.S. patent applicationSer. No. 15/799,792, filed on 31 Oct. 2017, which is acontinuation-in-part application of U.S. patent application Ser. No.15/351,016, filed on 14 Nov. 2016, which claims the benefit of U.S.Provisional Application No. 62/255,401, filed on 14 Nov. 2015, each ofwhich are incorporated in its entireties by this reference.

TECHNICAL FIELD

This invention relates generally to the field of electroencephalographyand more specifically to a new and useful system and method for testingcontact quality of electrical-biosignal electrodes in the field ofelectroencephalography.

BRIEF DESCRIPTION OF THE FIGURES

FIG. 1 is a flowchart representation of a method;

FIGS. 2A, 2B, and 2C are flowchart representations of variations of themethod;

FIG. 3 is a schematic representation of a system;

FIG. 4 is a schematic representation of one variation of the system;

FIG. 5 is a schematic representation of one variation of the system;

FIG. 6 is a flowchart representation of one variation of the method;

FIG. 7 is a flowchart representation of one variation of the method; and

FIG. 8 is a flowchart representation of one variation of the method.

DESCRIPTION OF THE EMBODIMENTS

The following description of embodiments of the invention is notintended to limit the invention to these embodiments but rather toenable a person skilled in the art to make and use this invention.Variations, configurations, implementations, example implementations,and examples described herein are optional and are not exclusive to thevariations, configurations, implementations, example implementations,and examples they describe. The invention described herein can includeany and all permutations of these variations, configurations,implementations, example implementations, and examples.

1. Methods

As shown in FIGS. 1 and 2B, a method for testing contact quality ofelectrical-biosignal electrodes includes: outputting a drive signalthrough a driven electrode no in Block S110, the drive signal includingan alternating-current component oscillating at a reference frequencyand a direct-current component; reading a reference signal from areference electrode 120 in Block S120; in response to the raw referencesignal excluding a first signal component oscillating at the referencefrequency and excluding a second signal component oscillating at anambient frequency, determining that the reference electrode 120 is inimproper contact with a user's skin in Block S122; in response to theraw reference signal excluding the first signal component oscillating atthe reference frequency and including the second signal componentoscillating at the ambient frequency, determining that the drivenelectrode 110 is in improper contact with the user's skin in Block S124;reading a first sense signal from a first sense electrode 131 in BlockS130; in response to the raw reference signal including the first signalcomponent oscillating at the reference frequency and in response to thefirst sense signal excluding a third signal component oscillating at thereference frequency, determining that the first sense electrode is inimproper contact with the user's skin in Block S132; and in response todetermination of improper contact between the user's skin and one of thedriven electrode 110, the reference electrode 120, and the first senseelectrode, generating an electrode adjustment prompt in Block S140.

One variation of the method shown in FIG. 2C includes: outputting adrive signal through a driven electrode in Block S110, the drive signalincluding an alternating-current component oscillating at a referencefrequency and a direct-current component; reading a set of sense signalsfrom a set of sense electrodes, the set of sense signals including afirst sense signal detected by a first sense electrode in the set ofsense electrodes in Block S130; calculating a combination of the set ofsense signals in Block S121; in response to the combination excluding afirst signal component oscillating at the reference frequency andincluding a second signal component oscillating at an ambient frequency,determining that the driven electrode is in improper contact with auser's skin in Block S124; in response to the combination including thefirst signal component oscillating at the reference frequency and inresponse to the first sense signal excluding a third signal componentoscillating at the reference frequency, determining that the first senseelectrode is in improper contact with the user's skin in Block S132; andin response to determination of improper contact between the user's skinand one of the driven electrode and the first sense electrode,generating an electrode adjustment prompt in Block S140.

Another variation of the method shown in FIG. 2C includes: receivingselection of a set of channels of interest in Block S170; selecting afirst subset of sense electrodes, in a set of sense electrodesintegrated into an electroencephalography headset, corresponding to theset of channels of interest in Block S170; selecting a second subset ofsense electrodes, in the set of sense electrodes, differing from thefirst subset of sense electrodes in Block S170; during a test period,outputting a drive signal through a driven electrode integrated into theelectroencephalography headset in Block S110, the drive signal includingan alternating-current component oscillating at a reference frequencyand a direct-current component; and, over a first duration of a testperiod, reading a first set of sense signals from the first subset ofsense electrodes in Block S130, reading a second set of sense signalsfrom the second subset of sense electrodes in Block S120, adjusting thedirect-current component of the drive signal to follow a firstcombination of the first subset of sense signals in Block S160,calculating a virtual reference signal as a function of the second setof sense signals in Block S121, and recording differences between thefirst set of sense signals and the virtual reference signal in BlockS150.

2. Applications

Generally, the method S100 can be implemented by an electrical biosignalacquisition system 100 to systematically characterize the quality ofcontact between electrodes—in the electrical biosignal acquisitionsystem 100—and a user's skin and to automatically provide guidance forimproving such contact quality, such as to a technician overseeing theuser or to the user directly. In particular, the electrical biosignalacquisition system 100 executing the method S100 can output a drivesignal containing an AC component through the driven electrode 110 incontact with the user's skin and then determine the quality of contactbetween the user's skin and the driven electrode 110, the referenceelectrode 120, and a set of sense electrodes based on the presence of alike AC component in raw reference and sense signals collected by thereference and sense electrodes, respectively. The driven electrode 110can output a drive signal containing an AC component oscillating at afrequency distinct from a frequency of common ambient electromagneticnoise (e.g., 60 Hz continuous AC noise in North America, 50 Hzcontinuous AC noise in Europe) and unique to oscillating electricalsignals generated by a living (e.g., human) body such that alternatingcomponents in each of the raw reference and sense signals can becorrelated with (e.g., matched to) the AC component of the drivesignal—entering the body at the driven electrode 110—with a high degreeof accuracy. For example, the electrical biosignal acquisition system100 can output a drive signal containing a DC component of 2.5V and anAC component characterized by a sinusoidal, 2.0 Hz, 1.7-millivoltpeak-to-peak AC signal; and the electrical biosignal acquisition system100 can correlate the presence of a 2.0 Hz AC signal in each of the rawreference and sense signals with the quality of contact between theuser's skin and the reference and sense electrodes, respectively.

In one example, Blocks of the method S100 can be executed by anelectroencephalogram (EEG) headset including 19 sense electrodes, onedriven (e.g., “driven right leg”) electrode, and one reference electrode120, as described below, to determine whether the sense, driven, andreference electrode are in proper contact with a patient's skin duringadministration of an EEG test. In this example, the EEG headset 102 candrive the driven electrode 110 at a reference frequency of 2.0 Hz andcan determine: that the driven electrode 110 is in improper contact withthe patient's (i.e., a user's) skin in Block S124 when the raw referencesignal excludes a 2.0 Hz component but includes a 60 Hz component (acommon ambient electromagnetic noise signal in North America); that thereference electrode 120 is in improper contact with the patient's skinin Block S122 when the raw reference signal excludes both a 2.0 Hzcomponent and a 60 Hz component; and that a particular sense electrode131 is in improper contact with the patient's skin in Block S132 whenthe driven and reference electrode are determined to be in propercontact with the patient's skin and when a sense signal output by theparticular sense electrode 131 excludes a 2.0 Hz component (or whencomposite sense signal—including the raw reference signal subtractedfrom the raw sense signal—includes the 2.0 Hz component”). In thisexample, the EEG headset 102 can then broadcast a notification to anexternal connected device (e.g., a smartphone or tablet carried by anurse, doctor, therapist, or epileptologist, etc. administering the EEGtest) to notify an EEG test administrator of improper contact between aparticular electrode and the patient's skin (hereinafter a “contact lossevent”). In this example, the EEG headset 102 can additionally oralternatively flag or annotate data collected through each senseelectrode 131 during an EEG test with the determined contact states ofthe driven electrode 110, reference electrode 120, and sense electrodes.

The EEG headset 102 can also implement Blocks of the method to calculatea “virtual” reference signal from one, a subset, or all active senseelectrodes integrated into the EEG headset 102, thereby reducing a totalnumber of electrodes in the EEG headset 102 and reducing complexity inmanufacture and setup of the EEG headset 102 on a user's head.Furthermore, the EEG headset 102 can selectively activate a subset ofsense electrodes during an EEG test, such as a first subset of senseelectrodes that correspond to channels of interest specified in an EEGtest configured by an EEG test administrator. During this EEG test, theEEG headset 102 can record sense signals read by this first subset ofsense electrodes to a digital file to the exclusion of other senseelectrodes in the EEG headset 102. The EEG headset 102 can alsoselectively activate a second subset of sense electrodes during the EEGtest, transform sense signals read from this second subset of senseelectrodes into a virtual reference signal, analyze the virtualreference signal to confirm that the driven electrode is in propercontact with the user's skin, and reject noise in the channels ofinterest by subtracting the virtual reference signal from sense signalsread from the first subset of sense electrodes.

The EEG headset 102 can also regularly adjust the DC component of thedrive signal output by the driven electrode to follow the average centervoltage of the sense electrodes in order to center these sense signalswithin the dynamic range of these sense electrodes. Therefore, the EEGheadset 102 can execute Blocks of the method to selectively activate anddeactivate sense electrodes, to selectively record sense signalscorresponding to channels of interest, to selectively calculate virtualreference signals from multiple sense signals (e.g., corresponding ornot corresponding to channels of interest), and to dynamically adjustthe DC component of the drive signal to follow sense signals read fromthese sense electrodes (corresponding to channels of interest), therebyrejecting noise in recorded signals while also limiting rejection ofrelevant signals, ensuring that that peak-to-peak voltages at each senseelectrode remain within the dynamic range of the sense electrodes (i.e.,preventing “clipping”), and maintaining high signal quality during anEEG test.

The method S100 is described herein as executed by an EEG headset 102.For example, an EEG headset 102 can execute Blocks of the method S100 todetect and actively handle contact loss events by notifying an EEG testadministrator of changes in contact quality at all or select electrodessubstantially in real-time. The EEG headset 102 can additionally oralternatively handle contact loss events passively by annotating datacollected by the sense (and reference) electrodes with contact lossevents. However, the method S100 can be similarly executed by anelectrocardiogram (ECG) system, an electromyogram (EMG) system, amechanomyogram (MMG) system, an electrooculography (EOG) system, agalvanic skin response (GSR) system, and/or a magnetoencephalogram(MEG), etc.

3. System

As shown in FIGS. 3, 4, and 5 , the method S100 can be executed by anelectrical biosignal acquisition system 100, including: a drivenelectrode 110 electrically configured to contact skin of a user remotelyfrom an area of interest; a signal generator 140 configured to output adrive signal oscillating at a reference frequency about a center voltageinto the user via the driven electrode no; a reference electrode 120configured to contact skin of the user remotely from the area ofinterest and to detect a raw reference signal; a first sense electrode131 configured to contact skin of the user at the area of interest andto detect a first raw sense signal from the area of interest; and asupport structure 104 configured to support the driven electrode 110,the reference electrode 120, and the first sense electrode 131 on theuser. The electrical biosignal acquisition system 100 also includes asignal processor 150 configured to: transform absence of a first signalcomponent oscillating at the reference frequency in the raw referencesignal and absence of a second signal component oscillating at anambient frequency from the raw reference signal into confirmation thatthe reference electrode 120 is in improper contact with the user's skin;transform absence of the first signal component oscillating at thereference frequency and presence of the second signal componentoscillating at the ambient frequency in the raw reference signal intoconfirmation that the driven electrode 110 is in improper contact withthe user's skin; and to transform confirmation that the referenceelectrode 120 is in proper contact with the user's skin, confirmationthat the driven electrode 110 is in proper contact with the user's skin,and absence of a third signal component oscillating at the referencefrequency from the first raw sense signal into confirmation that thefirst sense electrode 131 is in improper contact with the user's skin.(Similarly, the signal processor 150 can transform confirmation that thereference electrode 120 is in proper contact with the user's skin,confirmation that the driven electrode 110 is in proper contact with theuser's skin, and presence of a third signal component oscillating at thereference frequency in a first composite sense signal—representing adifference between the raw reference signal output by the referenceelectrode and the raw sense signal output by the first senseelectrode—into confirmation that the first sense electrode 131 is inimproper contact with the user's skin.)

The electrical biosignal acquisition system 100 is described herein asdefining an EEG headset 102 configured to collect neural oscillation (or“brain wave”) data from one or more sense electrodes when worn by auser. However, the electrical biosignal acquisition system 100 caninclude any other suitable type of biosensor electrode system. Theelectrical biosignal acquisition system 100 can also include one or morecontact-based or non-contact sensors and can implement methods andtechniques described herein to collect, process, and handle any suchcontact-based or non-contact sensor data.

4. Signal Generator and Driven Electrode

The signal generator 140 of the EEG headset 102 is configured to outputa drive signal that includes a DC component and an AC componentoscillating at a reference frequency; and the driven electrode 110 iselectrically coupled to the signal generator 140, is configured tocontact skin of a user, and outputs the drive signal into the user'sskin. Generally, the signal generator 140 generates a drive signal thatthe driven electrode no then communicates into the body of the user toestablish a known (or “reference”) potential at the user's body relativeto a power supply (e.g., a battery ground) within the EEG headset 102.

In one implementation, the EEG headset 102 includes a cage configured tosupport the driven electrode no against the user's skin but remotelyfrom the user's head where electrical signals from brain activity (i.e.,neural oscillations) predominate. For example, as shown in FIG. 5 , thecage can include a beam extending downward from the top of the EEGheadset 102, supporting the driven electrode no, and configured tocompress the driven electrode no against the right side of the user'sneck when the EEG headset 102 is worn by the user. Alternatively, thedriven electrode 110 can be mounted to the interior surface of a springclip and connected to the cage via a flexible hookup wire, and thespring clip can be manually opened and released onto the user's rightear lobe after the EEG headset 102 is installed on the user's head.

The EEG headset 102 can also include a battery 170, and the signalgenerator 140 and the battery 170 can be arranged within a housingsupported above or within the cage. The signal generator 140 can sourcecurrent from the battery 170, convert this current into a drive signaloscillating at a reference frequency about a center voltage (e.g., asinusoidal, 2.0 Hz, 1.7 millivolt peak-to-peak AC signal on a static ordynamic DC component of 2.5V), and then output this drive signal to thedriven electrode 110 via a hookup wire, as shown in FIG. 3 . The signalgenerator 140 and the driven electrode 110 can therefore cooperate toexecute Block S110 of the method S100.

5. Reference Electrode

The reference electrode 120 is configured to contact skin of the userand to collect a reference signal from the user's body. Generally, thereference electrode 120 functions to conduct a reference signal from theuser's skin into the signal processor 150, which then analyzes the rawreference signal to confirm connectivity (e.g., contact) between theuser's skin and the driven electrode 110, the reference electrode 120,and one or more sense electrodes according to the method S100. Thesignal processor 150 within the EEG headset 102 can also implementcommon-mode rejection techniques to remove noise (e.g., artifacts) fromsense signals collected by the sense electrodes by subtracting the rawreference signal from each raw sense signal in Block S131, as describedbelow and shown in FIG. 2 .

In one implementation, shown in FIGS. 3, 4, and 5 , the referenceelectrode 120 includes a dry EEG electrode including: a substrate; a setof electrically-conductive prongs extending from a first side of thesubstrate; and an amplifier coupled to the substrate opposite the set ofprongs and configured to amplify an electrical signal detected by theset of prongs. The electrically-conductive prongs can be elastic (e.g.,gold-plated silicone bristles) or rigid (e.g., gold-plated copperprongs). The reference electrode 120 can alternatively include a flat ordomed contact disk configured to contact the user's skin. Alternatively,the reference electrode 120 can be configured to accept interchangeable(e.g., magnetic) contact inserts, such as one of an elastic bristleinsert, a rigid prong insert, a flat contact disk insert, and a domedcontact disk insert.

In this implementation, the amplifier can include a differential op-ampincluding: a non-inverting input electrically coupled to the substrate;and an inverting input that receives the DC component of the drivesignal from a DC output channel of the signal generator 140, as shown inFIG. 3 . The amplifier can subtract the DC component of the drive signalfrom a high-impedance reference signal detected at the prongs, amplifythe result (e.g., by a gain of 10, 1,000, or 100,000), and output theamplified result as a low-impedance reference signal that follows thehigh-impedance reference signal less the DC component of the drivesignal and amplified by a gain value greater than 1. In thisimplementation, the output of the amplifier can be connected to thesignal processor 150, which can receive the low-impedance referencesignal from the reference electrode 120 and process this low-impedancereference signal to determine the contact state of the reference anddriven electrode, as in Blocks S122 and S124, respectively.

Alternatively, the reference electrode 120 can include a non-invertingop-amp in a closed-feedback configuration characterized by a gain of ˜1and including a non-inverting input electrically coupled to thesubstrate in the reference electrode 120. In this example, the amplifiercan include a buffer or a voltage follower (as shown in FIG. 4 ) and canreceive a high-impedance reference signal from the set of prongs andoutput a low-impedance reference signal that follows the high-impedancereference signal directly. However, the reference electrode 120 caninclude any other type of dry- or wet-type EEG electrode.

Like the driven electrode 110 described above, the EEG headset 102 cansupport the reference electrode 120 against the user's skin and remotelyfrom the user's head where electrical signals from brain activity aremost present. In particular, because the signal processor 150 removesthe raw reference signal from raw sense signals to form composite sensesignals, the EEG headset 102 can support the reference electrode 120against the user's skin substantially remotely from the sense electrodesand from the user's scalp, thereby minimizing collection of neuraloscillations (e.g., “brain waves”) by the raw reference signal, whichwould otherwise be rejected from the composite sense signals when theraw reference signal is subtracted from the raw sense signals in BlockS131, as described below. For example and as shown in FIGS. 1 and 5 ,the case of the EEG headset 102 can include a second beam extendingdownward from the top of the EEG headset 102, supporting the referenceelectrode 120 opposite the driven electrode 110, and configured tocompress the reference electrode 120 against the left side of the user'sneck when the EEG headset 102 is worn by the user. Alternatively, likethe driven electrode 110, the reference electrode 120 can be mounted tothe interior surface of a second spring clip and connected to the cagevia a second flexible hookup wire, and the second spring clip can bemanually opened and released onto the user's ear left lobe after the EEGheadset 102 is installed on the user's head.

Therefore, the driven electrode no can output a drive signal—includingan AC component and a DC component—to establish a known, oscillatingpotential in the user's body during an EEG test in Block S110. When incontact with the user's skin during the EEG test, the referenceelectrode 120 detects the drive signal, ambient noise, and/or otherextraphysiologic artifacts and outputs these as a singular referencesignal to the signal processor 150 in Block S120.

6. Sense Electrode

The EEG headset 102 also includes a sense electrode 131 configured tocontact skin of the user and to pass neural oscillation data in the formof a sense signal from the user's skin into the signal processor 150. Inthe implementation described above in which the EEG headset 102 includesa cage, the cage can also support one or more sense electrodes 130 andcan compress the sense electrodes 130 against the user's scalp when theEEG headset 102 is worn on the user's head. For example, the EEG headset102 can include 19 sense electrodes 130 arranged in a 10-20configuration, including two sense electrodes supported across a frontalpolar site, four sense electrodes supported across a frontal lobeposition, four sense electrodes supported across a temporal lobeposition, five sense electrodes supported across lateral andlongitudinal center axes, two sense electrodes supported across aparietal lobe position, and two sense electrodes supported across anoccipital lobe position by the cage. However, the EEG headset 102 caninclude any other number of sense electrodes arranged in any otherformat or configuration.

Each sense electrode in the set of sense electrodes 130 can define a dryEEG electrode substantially similar to the reference electrode 120, suchas including: a substrate; a set of electrically-conductive prongsextending from a first side of the substrate; and an amplifier coupledto the substrate opposite the set of prongs and configured to amplify anelectrical signal passing through the set of prongs. Like the referenceelectrode 120 described above, when the EEG headset 102 is worn by theuser, a sense electrode 131 can: contact the user's scalp; detect ahigh-impedance sense signal from the user's skin; convert thehigh-impedance sense signal into a low-impedance sense signal less theDC component of the drive signal (e.g., at a differential op-amp); andpass the low-impedance sense signal to the signal processor 150. The setof sense electrodes 130 can therefore be substantially similar, and eachsense electrode 131 can be substantially similar to the referenceelectrode 120 such that the group of reference and sense electrodesoutput signals exhibiting similar gains, latencies, extraphysiologicartifacts, and/or intraphysiologic artifacts, etc.

However, the EEG headset 102 can include any other number and type ofdry or wet sense electrodes.

7. Signal Processor

The EEG headset 102 also includes a signal processor 150 configured to:subtract a component of a raw reference signal output by the referenceelectrode 120 from a raw sense signal output by the sense electrode 131to calculate a composite sense signal for the sense electrode 131 inBlock S131; and to determine quality of contact between the drivenelectrode 110, the reference electrode 120, and each sense electrode 131in the set of sense electrodes 130 based on the presence of componentsoscillating at the ambient frequency in the raw reference signal andbased on presence of components oscillating at the reference frequencyin the raw reference signal and in the sense signals. Generally, thesignal processor 150 functions: to receive a raw reference signal fromthe reference electrode 120 and a raw sense signal from each of one ormore sense electrodes in Blocks S120 and S130, respectively; todetermine connectivity between the user's skin and the driven andreference electrode based on stability (or presence) of one or more ACcomponents in the raw reference signal in Blocks S124 and S122,respectively; and—once the drive and reference electrodes are determinedto be in proper contact with the user's skin—to determine connectivitybetween the user's skin and a sense electrode 131 based on the presenceof an AC component characterized by the reference frequency in acorresponding raw sense signal (or absence of the AC component acorresponding composite sense signal) in Block S132.

In one implementation, the signal processor 150 includes an(multi-channel) analog-to-digital converter (ADC) that transforms a raw,low-impedance analog reference signal received from the referenceelectrode 120 into a raw digital reference signal (i.e., a digital valuerepresenting a voltage on the output channel of the reference electrode120 for each sampling period). The signal processor 150 then computes afrequency (e.g., Fourier) transform of the digital reference signal,such as for a sampling period including one, two, four, or other numberof cycles of the reference frequency. For example, for a referencefrequency of 2.0 Hz, the signal processor 150 can compute the Fouriertransform of the digital reference signal over a one-second samplingperiod, which may include two cycles of the AC component of the drivesignal if the driven and reference electrode are in proper contact withthe user's skin. In particular, if the frequency transform of thedigital reference signal includes an AC component at the referencefrequency, the signal processor 150 can determine that the driven andreference electrode are properly coupled via the user's skin and aretherefore in proper contact with the user's skin for the samplingperiod. However, if the frequency transform of the digital referencesignal excludes an AC component at the reference frequency, the signalprocessor 150 can determine that the driven and reference electrode arenot properly coupled through the user and therefore that either or boththe driven electrode 110 and the reference electrode 120 are not inproper contact with the user's skin.

In the foregoing implementation, if the frequency transform of thedigital reference signal excludes both a first AC component at thereference frequency and a second AC component characterized by a commonambient electromagnetic noise frequency (e.g., 60 Hz in North America),the signal processor 150 can determine that the reference electrode 120is in improper contact with the user's skin in Block S122. For example,the user's body may function as an RF collector (e.g., an “antenna”)that collects ambient electromagnetic noise and communicates thiselectromagnetic noise into the reference electrode 120 when thereference electrode 120 is in proper contact with the user's skin.Therefore, for the EEG headset 102 used indoors in a lighted room inNorth America, if an oscillating (e.g., sinusoidal) 60 Hz signalcomponent is not detected in the digital reference signal, the signalprocessor 150 can determine that (at least) the raw reference signal isin improper contact with the user's skin in Block S122.

However, if the frequency transform of the digital reference signalexcludes an AC component at the reference frequency but includes an ACcomponent at a frequency of persistent ambient electromagnetic noise,the signal processor 150 can determine that the driven electrode 110 isin improper contact with the user's skin in Block S124. In particular,for the EEG headset 102 used indoors in a lighted room in North America,if the reference electrode 120 is in proper contact with the user's skinbut the driven electrode 110 is not, the digital reference signal mayinclude a sinusoidal 60 Hz signal component but may exclude an ACcomponent like the AC component output by the drive signal. The signalprocessor 150 can therefore determine the contact state of the drivenelectrode 110 in Block S124 based on the presence of (or lack of)certain AC signals in the raw reference signal.

For each sampling period during an EEG test, the ADC can also transforma raw, low-impedance analog sense signal received from a sense electrode131 into a raw digital sense signal (i.e., a digital value representinga voltage on the output channel of the sense electrode 131 for eachsampling period). The signal processor 150 can then subtract a digitalvalue (e.g., a 32-bit value) of the digital reference signal from adigital value (e.g., also a 32-bit value) of the digital sense signalfor the same sampling period to calculate a composite digital sensesignal representing a voltage at the input side of the sense electrode131 (i.e., a neural voltage relative to the reference signal) for thesampling period in Block S131. The signal processor 150 can repeat thisprocess for each sense electrode 131 to calculate one composite digitalsense signal per sense electrode 131 per sampling period during the EEGtest.

Alternatively, the signal processor 150 can subtract the raw,low-impedance analog reference signal from the raw, low-impedance analogsense signal to calculate a composite analog sense signal in Block S131and then pass this composite analog sense signal through the ADC. Forexample, each sense electrode 131 can include a differential op-amp:including an inverting input electrically connected to the output of thereference electrode 120; a non-inverting input electrically connected tothe output of the sense electrode 131; and an output feeding into onechannel of the ADC. In this example, the ADC can thus transform anoutput of the differential op-amp connected to the sense electrode 131(i.e., a “composite analog sense signal”) directly into a compositedigital sense signal. The signal processor 150 can repeat this processfor each sense electrode 131 to calculate one composite digital sensesignal per sense electrode 131 per sampling period during the EEG test.

Because the raw reference signal and a raw sense signal output by aparticular sense electrode 131 may include common ambient noise andother extraphysiologic and/or intraphysiologic artifacts, the signalprocessor 150 can achieve common-mode rejection by subtracting the rawreference signal (in raw low-impedance analog form or in raw digitalform) from the raw sense signal for the particular sense electrode 131in Block S131, thereby improving the signal-to-noise ratio (SNR) foreach sense channel. Furthermore, because the reference electrode 120 isconfigured to contact the user's skin remotely from the scalp or otherregion of the user's head in which neural oscillations are commonlypresent (or present in greater amplitude), the raw reference signal mayexclude a neural oscillation component or include only a very minorneural oscillation component such that neural oscillations in thecomposite sense signal are not rejected when the raw reference signal issubtracted from the sense signal in Block S131.

For each sense electrode 131, the signal processor 150 can then computea frequency transform of the composite digital sense signal (e.g., for asequence of composite digital sense signals over a period of time). Inthis implementation, if the driven and reference electrode aredetermined to be in proper contact with the user's skin, as describedabove, and if the frequency transform of the composite digital sensesignal corresponding to a particular sense electrode 131 excludes an ACcomponent at the reference frequency, the signal processor 150 candetermine that the particular sense electrode 131 is in proper contactwith the user's skin for the sampling period. In particular, the drivenand sense electrodes couple via the user's body when both are in propercontact with the user's skin; the raw, low-impedance sense signal outputby the sense electrode 131 therefore includes an AC component at thereference frequency when the drive and sense electrodes are in propercontact. When the reference electrode 120 is also in proper contact withthe user's skin, the low-impedance reference signal output by thereference electrode 120 similarly includes an AC component at thereference frequency; therefore, when the low-impedance reference signalis subtracted from the raw, low-impedance sense signal in Block S131 andthe result converted to digital form, the resulting composite digitalsense signal excludes an AC component at the reference frequency. Inparticular, in Block S136, the signal processor 150 can determine that asense electrode is in proper contact with the user's skin when: properskin contact at the driven electrode is confirmed in Block S126; properskin contact at the reference electrode is confirmed in Block S126; andthe frequency transform of the composite digital sense signal of thesense electrode—calculated by subtracting the low-impedance referencesignal from the low-impedance sense signal and digitizing the result inBlock S131—excludes an AC component at the reference frequency, as shownin FIG. 2A.

However, if the driven and reference electrode are determined to be inproper contact with the user's skin and the frequency transform of thecomposite digital sense signal includes an AC component characterized bythe reference frequency (which will be phased 180° from the AC componentof the drive signal), the signal processor 150 can determine that thesense electrode 131 is not in proper contact with the user's skin inBlock S132, as shown in FIG. 2A. In particular, when the sense electrode131 is not in proper contact with the user's skin, the raw,low-impedance sense signal output by the sense electrode 131 excludes anAC component at the reference frequency. When the reference electrode120 is in proper contact with the user's skin, the low-impedancereference signal output by the reference electrode 120 does include anAC component at the reference frequency; when the raw, low-impedancereference signal is then subtracted from the raw, low-impedance sensesignal in Block S131 and the result digitized, the resulting compositedigital sense signal includes an AC component at the reference frequencybut phased at 180° from the drive signal, which the signal processor 150can then interpret as improper contact between the user's skin and thesense electrode 131 in Block S132, as shown in FIG. 2A.

Therefore: an amplifier integrated into the reference electrode 120 canoutput a low-impedance reference signal that follows a high-impedancereference signal detected by prongs (or other contact surface) on thereference electrode 120; and the signal processor 150 can subtract a DCcomponent of the drive signal from the low-impedance reference signaland represent this difference in a composite digital reference signal(e.g., as one digital value per sampling period) in Block S131. Thesignal processor 150 can then decompose the composite digital referencesignal into a first set of oscillating signal components, such as byimplementing frequency analysis techniques substantially in real-time toprocess a set of digital values representing the composite digitalreference signal over a contiguous sequence of sampling periods. Thesignal processor 150 can then determine that the reference electrode 120is in improper contact with the user's skin in Block S122 if the firstset of oscillating signal components excludes both a first signalcomponent oscillating at the reference frequency (e.g., 2 Hz) and asecond signal component oscillating at an ambient frequency (e.g.,approximately 60 Hz in North America, 50 Hz in Europe). Similarly, thesignal processor 150 can determine that the driven electrode 110 is inimproper contact with the user's skin in Block S124 if the first set ofoscillating signal components excludes the first signal componentoscillating at the reference frequency but includes the second signalcomponent oscillating at the ambient frequency. However, the signalprocessor 150 can determine that the driven electrode 110 and thereference electrode 120 are in proper contact with the user's skin inBlock S126 if the first set of oscillating signal components—extractedfrom the digital reference signal—includes the first signal componentoscillating at the reference frequency.

Furthermore: an amplifier integrated into a sense electrode 131 canoutput a raw, low-impedance sense signal that follows a raw,high-impedance sense signal detected by prongs (or a contact surface) onthe sense electrode 131; and the signal processor 150 can subtract theraw, low-impedance reference signal from the raw, low-impedance sensesignal in Block S131 and digitize this difference to create a compositedigital sense signal. (The signal processor 150 can alternativelysubtract one digital reference value of a raw digital reference signalfrom a digital sense value of a raw digital sense signal recorded duringthe same sampling period for each sampling period during operation ofthe EEG headset 102 to create a composite digital sense signal for thissense electrode in Block S131.) The signal processor 150 can thendecompose the composite digital sense signal into a second set ofoscillating signal components, such as by implementing frequencyanalysis techniques in real-time to process a set of digital valuesrepresenting the composite digital sense signal over a contiguoussequence of sampling periods. Once the signal processor 150 determinesthat the drive and reference electrode are in proper contact with theuser's skin, the signal processor 150 can then determine that the senseelectrode 131 is in improper contact with the user's skin in Block S132if the second set of oscillating signal components includes a thirdsignal component oscillating at the reference frequency (i.e., a thirdsignal component oscillating at the reference frequency and phased at180° from the AC component of the drive signal due to subtraction of theraw reference signal—containing a signal component oscillating at thereference frequency and in-phase within the drive signal—from the rawsense signal). However, the signal processor 150 can also determine thatthe sense electrode 131 is in proper contact with the user's skin inBlock S136 if the second set of oscillating signal components excludesthe third signal component oscillating at the reference frequency.

The signal processor 150 can test the skin connectivity of the drivenelectrode no, the reference electrode 120, and the set of senseelectrodes 130 serially and continuously throughout operation (e.g.,throughout an EEG test), as shown in FIGS. 2A and 2B. A controller 160can then handle detected loss of skin contact for all or a subset ofelectrodes in the EEG headset 102, as described below.

8. Virtual Reference Signal

One variation of the method shown in FIG. 2C includes: reading a secondset of sense signals from a second subset of sense electrodes in BlockS120; and calculating a combination of the set of sense signals andstoring this combination as a virtual reference signal in Block S121.Generally, in this variation, the EEG headset 102 (or the native EEGtest application described above) can generate a virtual referencesignal from one or more sense electrodes—rather than read a referencesignal from a dedicated reference electrode—and then implement methodsand techniques described above to detect contact loss at the drivenelectrode and to calculate composite sense signals based on this virtualreference signal.

In one implementation, the signal processor 150: reads a raw analogsense signal from each sense electrode in the EEG headset 102 during asampling period within an EEG test; transforms each raw analog sensesignal into a raw digital sense signal at the ADC; calculates acombination (e.g., an average) of all raw digital sense signals for thesampling period; and stores this combination as a virtual referencesignal for the sampling period. The signal processor 150 can thensubtract the virtual reference signal from each raw digital sense signalto calculate composite digital sense signals for the sampling period (orfor the next sampling period) and writes these composite digital sensesignals to memory in Block composite digital sense signals in BlockS150. The signal processor 150 can also analyze the virtual reference todetermine when the driven electrode is in proper contact with the user'sskin in Block S124, as described above. The signal processor 150 canrepeat this process for each subsequent sampling period during the EEGtest. The signal processor 150 can also fuse a previous virtualreference signal with raw digital sense signals detected during a nextsampling period in order to damp signal noise between these samplingperiods.

In a similar implementation, the signal processor 150 can calculate avirtual reference signal from sense signals read from a subset of senseelectrodes during an EEG test. For example, for an EEG test designatingthe frontal lobe as an area of interest, the EEG headset 102 can: definea first subset of sense electrodes that includes FP1, FP2, F7, F3, FZ,F4, and F8 electrodes arranged across a frontal lobe region of the EEGheadset 102; and define a second subset of sense electrodes thatincludes T5, P3, PZ, P4, and T6 electrodes arranged across temporal andparietal lobe regions of the EEG headset 102. In this example, the EEGheadset 102 can thus define distinct, non-overlapping subsets of senseelectrodes, wherein the first subset of sense electrodes span an area ofinterest on the user's scalp and wherein the second subset of senseelectrodes are remote from this area of interest and span a region ofthe human head commonly exhibiting relatively minimal muscle movement.During execution of this EEG test, the EEG headset 102 can: calculate avirtual reference signal from sense signals read from the second subsetof sense electrodes in Block S121; combine the virtual reference signalwith sense signals from the first subset of sense electrodes to rejectnoise from these channels of interest; and record these compositedigital sense signals from the first subset of sense electrodes to adigital file in Block S150 for subsequent analysis. By defining thesecond subset of sense electrodes that is distinct from the first subsetof sense electrodes, the EEG headset 102 can calculate a virtualreference signal that includes substantially identical noise componentsas sense signals from the first subset of sense electrodes but thatexcludes relevant signals read from the first subset of sense electrodesover the area of interest. The signal processor 150 can thus achievehigh selectivity in rejecting common mode noise from sense signals fromthe first subset of sense electrodes by subtracting the virtualreference signal from these sense signals. Similarly, by defining thesecond subset of sense electrodes over regions of the skull thatfrequently exhibit minimal muscle movement, the EEG headset 102 cancalculate a virtual reference signal that is relatively free of muscle-and/or movement-type noise and that therefore represents a relativelyhighly accurate reference potential on the user's scalp.

In another example, the signal processor 150 can: define a defaultsecond subset of sense electrodes including the FZ, CZ, and PZ electrodearranged along the top-centerline of the skull and spanning a region ofthe human head commonly exhibiting relatively minimal muscle movement;and calculate a virtual reference signal from sense signals read fromthese three sense electrodes. If the FZ electrode is determined to havelost contact with the user's skin in Block S132 during execution of theEEG test, the signal processor 150 can dynamically deactivate the FZelectrode and remove the FZ sense signal from calculation of the virtualreference signal. The signal processor 150 can also: regularlyreactivate, sample, and test the FZ electrode for return of propercontact, such as once per two-second interval; and reactive the FZelectrode and return the FZ sense signal to calculation of the virtualreference signal once proper contact between the FZ sense electrode andthe user's skin returns. However, in this example, if the CZ senseelectrode is determined to have lost contact with the user's skin inaddition to the FZ sense electrode, the signal processor 150 canselectively activate (if previously inactive) an adjacent senseelectrode (e.g., the C3 and/or C4 sense electrode), confirm contactquality of the sense electrode in Block S132, and inject a correspondingsense signal into calculation of the virtual reference signal. Thesignal processor 150 can therefore: dynamically remove sense signals ofsense electrodes that have lost contact with the user's skin fromcalculation of the virtual reference signal; dynamically activate andinject sense signals from sense electrodes into calculation of thevirtual reference signal; and dynamically deactivate sense electrodesbased on the contact quality of each of these sense electrodesdetermined in Block S132.

Therefore, the signal processor 150 can populate a second subset ofsense electrodes—for calculation of a virtual reference signal fromtheir corresponding sense signals—based on an area of interest orspecific channels of interest specified in a predefined or custom EEGtest selected by an EEG test administrator. In particular, the signalprocessor 150 can select a predefined second subset of sense electrodebased on a type of EEG test or a first set of sense electrodes selectedby the EEG test administrator. Alternatively, the signal processor 150can automatically select a custom second subset of sense electrodesbased on a standard or custom first subset of sense electrodes selectedfor the upcoming EEG test, such as based on preset rules for populatingthe second subset of sense electrodes.

The signal processor 150 can also implement Block S132 to identify senseelectrodes in the second subset of sense electrodes that have lostcontact with the user's skin. When the signal processor 150 determinesthat a sense electrode in this second subset of sense electrodes haslost contact with the user's skin, the signal processor 150 can remove acorresponding sense signal from calculation of the virtual referencesignal in Block S121 substantially in real-time and until proper contactbetween this sense electrode and the user's skin is reestablished andconfirmed.

However, the signal processor 150 can implement any other method ortechnique to calculate a virtual reference signal from a fixed ordynamic set of one or more sense electrodes in the EEG headset 102 inBlock S121. Furthermore, in this variation, the EEG headset 102 candefault to reading and manipulating a reference signal read from thededicated reference electrode 120, as described above; however, when thesignal processor 150 determines that the reference electrode 120 haslost contact with the user's skin, the signal processor can deactivatethe reference electrode 120 (or discard the reference signal read fromthe reference electrode 120) and dynamically transition to calculating avirtual reference signal from one or more sense signals in Block S121.

9. Controller

One variation of the EEG headset 102 further includes a controller 160that handles instances of improper or poor contact between the user'sskin and any of the drive, reference, and sense electrodes duringoperation (or “contact loss events”). Generally, the controller 160 canexecute Block S140 of the method S100, which recites: in response todetection of improper contact between the user's skin and one of thedriven electrode 110, the reference electrode 120, and the senseelectrode 131, broadcasting an electrode adjustment prompt to anexternal device.

9.1 Push Notifications

In one implementation, the EEG headset 102 also includes a wirelesscommunication module 162, as shown in FIG. 3 , configured to communicatewirelessly (e.g., directly or through a network, such as through theInternet or over a cellular network) with a smartphone, tablet,smartwatch, or other external wireless-enabled device carried oraccessible by a nurse, doctor, therapist, epileptologist, or other EEGtest administrator administering an EEG test with the EEG headset 102 tothe user. Before initiating an EEG test, the wireless communicationmodule 162 can connect wirelessly to an external device and can maintaina persistent wireless connection with the external device during the EEGtest. During the EEG test, the controller 160 can push notifications forcontact loss events, as described below, to the external devicesubstantially in real-time in order to prompt the EEG test administratorto quickly correct electrode contact issues. For example, the controller160 can push a notification in the form of a SMS text message or anin-application notification to the external device.

The external device can additionally or alternatively execute a nativeEEG test application including a virtual graphical representation of theEEG headset 102 and the drive, reference, and sense electrodes. In thisimplementation shown in FIG. 6 , the controller 160 can push electrodestatus updates to the external device—such as via a short-range wirelesscommunication protocol—substantially in real-time or in response to achange in the contact status of an electrode. Upon receipt of an updatefrom the EEG headset 102, the native EEG test application can update thevirtual graphical representation of the EEG headset 102 accordingly inorder to visually indicate the contact status of each electrode. Thenative EEG test application can then serve audible, visual, and/orhaptic prompts to the EEG test administrator to correct fitment of aparticular electrode on the user's scalp when a predefined trigger eventis detected, as described below.

The controller 160 can therefore selectively push notifications to theexternal device in response to detected contact loss events in BlocksS122, S124, and S132. Alternatively, the native EEG test applicationexecuting on the external computing device can regularly pull contactstates of electrodes in the EEG headset 102, such as once per second oronce per five-second interval, and implement methods and techniquesdescribed above and below to selectively serve prompts to the EEG testadministrator to correct skin contact at one or more electrodes in theEEG headset 102.

9.2 Electrode Adjustment Prompt

In one implementation, in response to a contact loss event, thecontroller 160 generates a notification that: identifies a specificelectrode that has lost contact with the user's skin; includes anidentifier of the EEG headset 102 worn by the user; and includes atextual and/or graphical prompt to restore proper contact between theuser's skin and the identified electrode by adjusting the EEG headset102. For example, if the driven electrode 110 is determined to be inimproper contact with the user's skin in Block S124, the controller 160can generate a notification including a graphical representation of theEEG headset 102 including the electrodes, can highlight the drivenelectrode 110 (e.g., in red) in the graphical representation of the EEGheadset 102, and can overlay a textual prompt reciting “Please depressthe driven electrode 110 on the right side of the patient's neck untilproper body contact is restored” over the graphical representation ofthe EEG headset 102.

In another implementation, the controller 160 can: generate anelectronic notification containing a prompt to correct contact between aparticular electrode—in the set of electrodes—determined to be out ofcontact with the user's skin (or out of contact with the user's skin formore than a threshold period of time); insert a virtual map of locationsof the set electrodes in the EEG headset 102 into the electronicnotification; and indicate the particular electrode within the virtualmap in Block S140. For example, if a Fp1 sense electrode 131 isdetermined to be in improper contact with the user's skin in Block S132,the controller 160 can: generate a notification including a graphicalrepresentation of the EEG headset 102 representing general positions ofelectrodes; highlight the Fp1 electrode (e.g., in red) in the graphicalrepresentation of the EEG headset 102; and insert a textual promptreciting “Please tighten the front adjustable headband on the headsetuntil contact at the Fp1 electrode is restored” over the graphicalrepresentation of the EEG headset 102 in Block S140.

In a similar implementation, each electrode in the EEG headset 102 canbe color-coded (or patterned) with a color (e.g., or pattern) uniquewithin the set of electrodes, and, in response to a contact loss eventat a particular electrode, the controller 160 can generate a contactloss notification identifying the particular electrode by its uniquecolor (or pattern). However, the controller 160 and/or the externaldevice can implement any other method or technique to notify an EEG testadministrator of a contact loss event.

9.2 Notification Timing

In this implementation, the controller 160 can also delay transmissionof a notification of a contact loss event at a particular electrodeuntil the particular electrode has been out of proper contact with theuser's skin for at least a threshold duration, a custom durationselected by the EEG test administrator, or a duration proportional tothe physical distance between the user and the EEG test administrator.For example, the controller 160 can track a duration of a contiguousperiod of time during which a first sense electrode 131 is determined tobe in improper contact with the user's skin; and then transmit anelectronic notification prompting adjustment of the first senseelectrode 131 to an external device accessible by anelectroencephalography test administrator if the duration of thecontiguous period of time exceeds a threshold duration, such as fiveseconds. In a similar example, the controller 160 can track a totalduration of time over which the first sense electrode 131 is determinedto be in improper contact with the user's skin since a last manualadjustment of the EEG headset 102 or within a preset interval (e.g., oneminute, five minutes); and then transmit an electronic notificationprompting adjustment of the first sense electrode 131 to the externaldevice in Block S140 if the total duration of time exceeds a thresholdduration, such as twenty seconds since the EEG headset 102 was lastadjusted by the EEG test administrator or ten seconds within a lastone-minute interval.

In another example, the controller 160 can track a total duration oftime during which sense electrodes across the set of sense electrodes130 are determined to be in improper contact with the user's skin (i.e.,a sum of the total time that each sense electrode 131 has been out ofcontact with the user's skin), such as since a last manual adjustment ofthe EEG headset 102 or within a preset interval; and then transmit, tothe external device, a second electronic notification prompting restartof the current EEG test substantially in real-time when this totalduration of time exceeds a second threshold duration (e.g., one minute,one minute within the last five minutes, or 5% of the total sensed timeacross the set of sense electrodes). (In a similar example, thecontroller 160 can determine asynchronously that insufficient data wascollected through electrodes during the EEG test, such as if the ratioof total time that a sense electrode 131 was in improper contact withthe user's skin to the total recorded data stream time across 19 senseelectrodes exceeds 5%, and then prompt the EEG test administrator torepeat the EEG test following its conclusion.) The controller 160 cantherefore selectively push a notification to an EEG test administrator(e.g., to a smartphone carried by the EEG test administrator or toanother external device accessible to the EEG test administrator) whenan amount of time that a single sense electrode 131 has been out ofcontact with the user's skin or when a total amount of time that senseelectrodes in the set have been out of contact with the user's skinexceeds a preset threshold time.

The controller 160 can implement similar methods and techniques to pushsuch a notification to the EEG test administrator if either the drivenelectrode 110 or the reference electrode 120 is determined to be out ofcontact with the user's skin. For example, because improper contactbetween the user's skin and either the driven electrode 110 or thereference electrode 120 may produce raw (or composite) sense signalsthat are unusable, the controller 160 can implement shorter thresholdtimes to trigger transmission of an electrode adjustment prompt to theEEG test administrator following detection of improper skin contact atthe drive and sense electrodes, such as: a contiguous two seconds ofimproper contact; five seconds of improper contact since a last manualadjustment of the EEG headset 102; or five seconds within a five minuteinterval.

9.4 Filtered Notifications

In a similar variation, the controller 160 responds to contact lossevents by selectively pushing notifications to the EEG testadministrator. In this variation, the controller 160 can withholdcontact loss notifications from an EEG test administrator based on atype of electrode that has lost contact, a total number of electrodesnot in proper contact at a particular instant in time, a total durationof time that one or a group of electrodes have been in improper contactwith the user's skin (as described above), and/or a type of EEG testbeing administered to the user, etc.

In one implementation, for a general EEG test in which the EEG headset102 is configured to record data from all channels (e.g., all 19electrodes in a 10-20 headset configuration) in the EEG headset 102, thecontroller 160 can push contact loss notifications to an EEG testadministrator substantially in real-time if either the driven electrode110 or the reference electrode 120 is determined to have lost contactwith the user's skin. However, the controller 160 can delay notifyingthe EEG test administrator of contact loss events at sense electrodesuntil a total number of sense electrodes simultaneously not in contactwith the user's skin surpasses a threshold electrode count (e.g., twoelectrodes, three electrodes). In one example, the controller 160 canimplement a static, preset threshold electrode count, or the thresholdelectrode count can be customized by the EEG test administrator, such asthrough the native EEG test application executing on an external device,such as a smartphone or tablet carried by the EEG test administrator. Inanother example, the controller 160 can dynamically adjust the thresholdnumber of electrodes based on a physical distance between the EEGheadset 102 and the external device. In this example, the controller 160and the wireless communication module 162 can cooperate to implementtime-of-flight techniques to estimate the distance between the EEGheadset 102 and the external device, and the controller 160 can adjustthe threshold electrode count—to trigger prompting the EEG testadministrator to correct a position of the EEG headset 102—proportionalto this determined distance. In this example, the controller 160 can setthe threshold electrode count to: null (i.e., zero electrodes) for adistance of less than five feet between the EEG headset 102 and theexternal device; one electrode for a distance of five feet to ten feetbetween the EEG headset 102 and the external device; two electrodes fora distance of ten feet to thirty feet between the EEG headset 102 andthe external device; three electrodes for a distance greater than thirtyfeet between the EEG headset 102 and the external device.

During execution of the EEG test at the EEG headset 102, the controller160 can implement definitions of “active” sense electrodes noted in theEEG test parameters to selectively filter contact loss events and toselectively issue notifications to the EEG test administrator (or to theuser, etc.) to correct contact between these active sense electrodes andthe user's skin. In particular, the controller 160 can: generate aprompt specifying adjustment of a first sense electrode 131 defined asrelevant (or “active”) for a type of the electroencephalography testcurrently underway at the EEG headset 102 in response to determinationof improper contact between the user's skin and the first senseelectrode 131 and then serve this prompt to the EEG test administrator,as described above; while also disregarding determination of impropercontact between the user's skin and a second sense electrode 132 definedas irrelevant (or “inactive”) for the type of electroencephalographytest currently underway at the EEG headset 102.

Alternatively, the controller 160 can set the signal processor 150 todeactivate (e.g., “ignore”) sense channels for sense electrodesdesignated as inactive (or not designated as active) during the EEGtest; the signal processor 150 can therefore not test inactive senseelectrodes for proper skin contact during the EEG test.

Yet alternatively, the signal processor 150 can continue to processsense signals from the inactive sense electrodes and predict futurecontact states at active sense electrodes based on determined skincontact states at inactive sense electrodes. For example, poor contactat an Fp1 electrode in a 19-sense-electrode EEG headset 102 may beindicative of poor skin contact—in the near future—at the Fp2 electrode(and vice versa). In this example, when executing a right-frontal-lobeEEG test in which sense signals from the Fp2, F4, and F8 electrodes arerecorded exclusively, the controller 160 can preempt contact loss at theFp2 by prompting the EEG test administrator to check the Fp2 electrodeif poor contact is detected at the Fp1 electrode, such as despitedetermination that the Fp2 electrode is currently in proper contact withthe user's skin. In this implementation, the controller 160 (or thenative EEG test application described above), can thus implement avirtual model of a mechanical structure of the EEG headset 102 and/or amodel or lookup table defining relationships between contact loss eventsat electrodes across the EEG headset 102 to predict future contact lossevents at active electrodes based on contact states of inactiveelectrodes.

Similarly, when prompting the EEG test administrator to correct contactat a particular (active) electrode due to contact loss at the particularelectrode, the controller 160 can also prompt the EEG test administratorto check other (active) electrodes—currently determined to be in propercontact but that have historically exhibited contact loss concurrentlywith contact loss at the particular electrode (e.g., as defined in thevirtual model of the EEG headset 102)—for proper contact when correctingthe particular electrode.

Yet alternatively, the signal processor 150 can process (raw orcomposite) sense signals from all sense electrodes and issue flags forcontact loss events for all sense electrodes, and the controller 160 cangenerate and transmit notifications for contact loss events at only theactive sense electrodes and discard (e.g., ignore) contact loss eventsfor inactive sense electrodes. However, the signal processor 150 and thecontroller 160 can cooperate in any other way to selectively activateand deactivate sense electrodes (or sense channels) and to selectivelyissue notifications for contact loss events at active sense electrodesduring an EEG test. The native EEG test application can similarlyselectively update a graphical representation of the EEG headset 102 toindicate contact states or contact loss events at active electrodes onlyand can selectively serve relevant prompts to the EEG test administrator(or to the user directly, as described below).

9.5 Adjustment Directives

In another variation, in Block S140, the controller 160 populates aprompt to correct skin contact at a particular electrode with adescription of a preferred or suggested mode of correction at theparticular electrode. In one implementation, in response to detection ofimproper contact between a first sense electrode 131 and the user'sskin, the controller 160: predicts an adjustment mode for the EEGheadset 102 to improve contact between the first sense electrode 131 andthe user's skin based on a virtual model of a mechanical structure ofthe EEG headset 102; inserts a description of the adjustment mode intoan electronic notification; and transmits the electronic notification toa local computing device.

In one example in which the EEG headset 102 includes a lower-rearheadband supporting T3, T5, O1, O2, T6, and T4 electrodes, if the signalprocessor 150 determines that at least three of these six electrodes onthe lower-rear headband are in improper contact at a particular instantin time or are exhibiting fluctuating contact states, the controller 160can: predict that the lower-rear headband is loose on the user's headbased on a virtual model of a mechanical structure of the EEG headset102, as described above; insert a prompt to tighten the lower-rearheadband into an electronic notification; and then transmit theelectronic notification to the external device for response by the EEGtest administrator. In a similar example, the EEG headset 102 includes:a lower-rear headband supporting T3, T5, O1, O2, T6, and T4 electrodes;a lower-front headband supporting F7, Fp1, Fp2, and F8 electrodes; acenter headband supporting C3, CZ, and C4 electrodes; and a center-frontheadband supporting F3, FZ, and F4 electrodes. In this example, if thesignal processor 150 determines that at least one of the C3, CZ, and C4electrodes and at least one of the F3, FZ, and F4 electrodes are inimproper contact at a particular instant in time or are exhibitingfluctuating contact states, the controller 160 can: predict that eitherthe lower-rear headband or the front-lower headband is too tight on theuser's head; insert a prompt to loosen the lower-rear and lower-frontheadbands into an electronic notification; and then transmit theelectronic notification to the external device for response by the EEGtest administrator.

In another example, the controller 160 can access a set of templateimages of contact states across electrodes in a like EEG headset 102,wherein each template image defines a (unique) combination of electrodesin proper and improper contact and is associated with a particularadjustment mode to correct electrodes in improper contact. In thisexample, the controller 160 can match an image of current contact statesacross electrodes in the EEG headset 102 to a particular template image,insert a description of the adjustment mode stored with the matchedtemplate image into an electronic notification, and then serve thisnotification to the EEG test administrator.

The controller 160 can thus implement: a virtual model of a mechanicalstructure of the EEG headset 102; a model or lookup table definingrelationships between contact states of groups of electrodes andadjustment of the support structure of the EEG headset 102; or astatistical model or table of common causes of contact loss events ofspecific electrodes; etc. to predict adjustment modes that will correctloss of skin contact at one or more electrodes in the EEG headset 102and then serve an electrode adjustment prompt containing a descriptionof this adjustment mode to the EEG test administrator in order tostreamline and guide manual adjustment of the EEG headset 102 inreal-time during an EEG test. However, the controller 160 (or the nativeEEG test application, etc.) can implement any other method or techniqueto transform the contact states of one or more electrodes in the EEGheadset 102 into a directed prompt to correct skin contact at theseelectrodes.

The controller 160 can also implement tiered adjustment modes whenserving guidance to the EEG test administrator for correct skin contactat an electrode. For example, for the reference electrode 120 determinedto be in poor contact with the user's skin (e.g., the user's rightearlobe or the right side of the user's neck), the controller 160 cansequentially serve guidance to the EEG test administrator to: jostle thereference electrode 120; then clean the user's skin at the location ofthe reference electrode 120 if poor skin contact persists afterjostling; then exchange a disk-shaped electrode tip for a bristleelectrode tip at the reference electrode 120 if poor skin contactpersists after cleaning; and finally to replace the reference electrode120 entirely if poor skin contact persists after exchanging electrodetips. In this example, the controller 160 can receive confirmation fromthe EEG test administrator that such guidance was followed andattempted, such as through the native EEG test application andsequentially step through such preplanned adjustment modes specific tothe reference electrode 120 (or generic to all electrodes in the EEGheadset 102). The controller 160 can also transmit updated notificationsor electrode contact states to the external device for presentation tothe EEG test administrator substantially in real-time. The controller160 can additionally or alternatively update lighted indicators(described below) integrated into the headset to visually indicatecontact states of the electrodes substantially in real-time. However,the controller 160 can serve any other guided and/or tiered prompts tothe EEG test administrator (or to the user directly) in any othersuitable way in Block S140.

9.6 Integrated Contact Quality Indicator

In one variation, the EEG headset 102 further includes a lightedindicator 164 adjacent each electrode and updates a state of eachlighted indicator 164 according to the contact state of itscorresponding electrode. For example, each electrode can include a red(i.e., single-color) LED opposite its set of prongs and electricallycoupled to a corresponding LED driver within the controller 160. In thisexample, the controller 160 can activate (i.e., turn ON) an LED in aparticular electrode when the particular electrode is determined to havelost contact with the user's skin in Block S122, S124, or S132. Inanother example, each electrode can include a multi-color LED oppositeits set of prongs; for each electrode in the EEG headset 102, thecontroller 160 can set the color of an LED on an electrode: to green ifcontact between the user's skin and the electrode is determined to beproper; to red if contact between the user's skin and the electrode isdetermined to be improper; and to yellow if contact between the user'sskin and the electrode is fluctuating between proper and improper (e.g.,at a rate between 0.1 Hz and 2 Hz). In a similar example, each electrodecan include a discrete red LED and a discrete, adjacent green LEDopposite its set of prongs; for each electrode in the EEG headset 102,the controller 160 can activate either the red LED or the green LEDbased on the skin contact state of the electrode.

In this variation, in Block S140, the controller 160 can: illuminate afirst lighted indicator—arranged in the EEG headset 102 adjacent thefirst sense electrode 131—in a first color to indicate improper contactbetween the user's skin and the first sense electrode 131 in response todetermination of improper contact between the user's skin and the firstsense electrode 131 in Block S132; and can illuminate a second lightedindicator—arranged in the EEG headset 102 adjacent the second senseelectrode 132—in a second color to indicate proper contact between theuser's skin and the second sense electrode 132 in response todetermination of proper contact between the user's skin and the secondsense electrode 132 in Block S136. The controller 160 can thusselectively illuminate lighted indicators 164 integrated into the EEGheadset 102 adjacent electrodes determined to be in poor contact withthe user's skin in order to visually indicate to the EEG testadministrator—directly on the EEG headset 102—which electrodes requireadjustment, such as in addition to transmitting an electrode adjustmentprompt to the external device associated with the EEG testadministrator. (The controller 160 can also selectively change colors ofor selectively adjust illumination patterns (e.g., blinking patterns) ofthese lighted indicators 164 to indicate their contact states.) Thecontroller 160 can similarly visually communicate to the user wearingthe EEG headset 102—such as while sitting before a mirror—whichelectrodes require correction, and the user can depress regions of thesupport structure near illuminated lighted indicators 164 (or red orblinking lighted indicators) directly to correct skin contact at theseelectrodes.

In the foregoing implementations, when lighted indicator 164 (e.g., anLED) adjacent an electrode is activated, electromagnetic radiationoutput by the lighted indicator 164 may produce an extraphysiologicartifact in the signal output by its corresponding (i.e., adjacent)electrode. However, the reference and sense signals collected by thereference and sense electrodes, respectively may include substantiallysimilar indicator-based extraphysiologic artifacts, which may be excludefrom each composite sense signal via common-mode rejection when the rawreference signal is subtracted from raw sense signals at the signalprocessor 150 in Block S131, as described above.

However, the controller 160 can modify a state of any other one or morelighted indicators 164 integrated into the EEG headset 102 in order tovisually indicate the contact state or contact quality of each electrodeon the user's skin.

9.7 User-Directed Notifications

In one variation, the controller 160 (or a native EEG test applicationexecuting on a computing device carried by or accessible to the user)can also serve a prompt to correct skin contact at an electrode directlyto the user. For example, the controller 160 (or the native EEG testapplication) can implement methods and techniques described above toupdate a lighted indicator integrated into the EEG headset 102 toindicate poor contact at a particular electrode adjacent the lightedindicator and then push a prompt to correct the particular electrode tothe user's smartphone, such as by depressing the particular electrode orby adjusting a headband supporting the particular electrode on theuser's head. While looking at a mirror, the user can thus adjust theparticular electrode accordingly. The controller 160 can thus serve aprompt directly to the user in order to reduce a burden on the EEG testadministrator to monitor the user or if the user is completing an EEGtest without the aid of an EEG test administrator (e.g., while at home).

The controller 160 can also selectively serve electrode adjustmentprompts to one of the user and the EEG test administrator based on atype of adjustment needed. For example, the controller 160 can serveprompts to correct electrodes exhibiting moderate contact quality—suchas characterized by contact quality oscillating between proper andimproper and improper for no more than ten seconds per twenty-secondinterval—to the user. In this example, the user can thus manuallydepress such an electrode with her finger to correct contact with theuser's skin. However, in this example, the controller 160 can serveprompts to correct electrodes exhibiting poor contact quality—such ascharacterized by improper contact for more than ten seconds pertwenty-second interval—exclusively to the EEG test administrator, assuch poor contact quality may require the EEG test administrator toclean the user's skin or replace an electrode tip.

However, the controller 160 (or native EEG test application) canimplement any other method or technique to serve electrode adjustmentprompts directly to the user.

9.8 Contact Loss Checks

In one variation, the EEG headset 102 checks an electrode previouslydetermined to have lost contact with the user's skin to confirm whethercontact has been reestablished.

In one implementation, the signal processor 150 deactivates a particularelectrode: in response to detecting that this particular electrode haslost contact with the user's skin in Block S122 or S134; in response tothe corresponding (raw or digital) sense signal differing from anaverage amplitude of all sensor signals by a threshold proportion (e.g.,100%) during the current sampling period; or in response to the averageamplitude of the corresponding (raw or digital) sense signal approachingeither voltage rail of the EEG headset 102 (e.g., 0V and V_(cc). In thisimplementation, the signal processor 150 intermittently reactivates thatparticular electrode, reads a sense signal from the particularelectrode, and analyzes the sense signal according to Block S134 todetermine whether a particular electrode has regained contact, such ason a regular interval of one per second or once per five-secondinterval. Thus, if the signal processor 150 determines that propercontact between the particular electrode and the user's skin hasreturned, the signal processor 150 can reactivate the particularelectrode; otherwise, the signal processor 150 can return the particularelectrode to the inactive state. While the particular electrode is inthe inactive state, the signal processor 150 can continue to sample theparticular electrode but discard this sense signal; alternatively, thesignal processor can deactivate the particular electrode by electricallydecoupling the particular electrode from the ADC or by otherwiseisolating the particular electrode from other sense electrodes in theEEG headset 102. Furthermore, while the particular electrode isdeactivated, the signal processor 150 can refrain from recording thecorresponding sense signal from the digital file in Block S150, refrainfrom incorporating the corresponding sense signal from calculation of avirtual reference signal in Block S121, and/or refrain fromincorporating the corresponding sense signal from calculation of a DCcomponent of the drive signal in Block S162 as described below. However,once proper contact between the particular electrode and the user's skinis reestablished, the signal processor 150 can return to recording thecorresponding sense signal in Block S150, incorporating thecorresponding sense signal into calculation of the virtual referencesignal in Block S121, and/or incorporate the corresponding sense signalinto calculation of the DC component of the drive signal in Block S162.For example, if the signal processor 150 determines that a first senseelectrode has lost contact with the user's skin at a first time, thesignal processor 150 can then: reactivate the first sense electrode at asecond time succeeding the first time by a preset check duration (e.g.,on a five-second interval); read a sense signal from the first senseelectrode; determine that the first electrode is in proper contact withthe user's skin at the second time if the sense signal includes a signalcomponent oscillating at the reference frequency; and maintain the firstelectrode in an active state following the second time if the firstelectrode is in proper contact with the user's skin.

The EEG headset 102 can additionally or alternatively implement theforegoing methods and techniques in response to receipt of confirmationfrom the EEG test administrator (or from the user) that a particularelectrode has been adjusted following transmission of an electrodeadjustment prompt specifying adjustment of the particular electrode. Forexample, the EEG test administrator can confirm response to an electrodeadjustment prompt through an instance of the native EEG test applicationexecuting on her mobile computing device; the native EEG testapplication can wirelessly transmit this confirmation to the EEG headset102; upon receipt of this confirmation, the signal processor 150 canimplement the foregoing methods and techniques to retest this senseelectrode. The controller 160 can then serve a notification to the EEGtest administrator confirming proper adjustment of the particularelectrode or prompting further adjustment if the controller 160determines that the particular electrode is still exhibiting poorcontact with the user's scalp.

However, the EEG headset 102 can respond to loss of contact between anelectrode and the user's skin in any other way and retest this contactin response to any other event or trigger.

9.9 Warnings

In one variation shown in FIG. 8 , the controller implements additionalchecks to determine whether a sense electrode is in proper contact withthe user's skin (e.g., exhibiting strong capacitive coupling to theuser's scalp), in poor contact with the user's skin (e.g., exhibitingpoor capacitive coupling to the user's scalp), or not in contact withthe user's skin (e.g., exhibiting no detectable capacitive coupling tothe user's scalp) and can serve notifications to the EEG testadministrator accordingly. For example and as shown in FIG. 8 , thecontroller can read a composite digital sense signal originating from asense electrode in Block S130 and then determine that the senseelectrodes is nearing saturation if the composite digital sense signalapproaches a saturation voltage (e.g., exceeds 300 mV for a saturationvoltage of 320 mV). If the sense electrode is nearing saturation but isnot saturated, the controller 160 can issue a warning for the senseelectrode; if the sense electrode is saturated, the controller 160 canflag the sense channel, issue a prompt to correct the sense electrode,and/or discard the composite digital sense signal for this samplingperiod.

However, if the sense electrode is not saturated, the controller 160 canthen check whether the composite digital sense signal contains acomponent oscillating at the reference frequency (e.g., 2 Hz). Inparticular, because the reference signal is subtracted from the sensesignal to produce the composite digital sense signal, the compositedigital sense signal may exclude this oscillating reference component ifboth the sense and reference electrodes are in proper contact with theuser's skin. Therefore, if the controller 160 determines that thecomponent in the composite digital sense signal oscillating at thereference frequency exhibits a peak-to-peak voltage greater than a lowthreshold reference voltage (e.g., 3 uVpp) but less than a highthreshold reference voltage (e.g., 6 uVpp), the controller 160 can issuea warning that the sense electrode may be in poor contact or losingcontact with the user's skin. Similarly, if the controller 160determines that the component in the composite digital sense signaloscillating at the reference frequency exhibits a peak-to-peak voltagegreater than the high threshold reference voltage, the controller 160can flag the sense channel, issue a prompt to correct the senseelectrode, and/or discard the composite digital sense signal for thissampling period.

However, if this oscillating component of the composite digital sensesignal is characterized by a peak-to-peak voltage less than the lowthreshold ambient voltage, the controller can then check whether thecomposite digital sense signal contains a component oscillating at theambient frequency (e.g., 60 Hz). In particular, because the referencesignal is subtracted from the sense signal to produce the compositedigital sense signal, the composite digital sense signal may excludethis oscillating ambient component if both the sense and referenceelectrodes are in proper contact with the user's skin. Therefore, if thecontroller 160 determines that the component in the composite digitalsense signal oscillating at the ambient frequency exhibits apeak-to-peak voltage greater than a low threshold ambient voltage (e.g.,10 uVpp) but less than a high threshold ambient voltage (e.g., 100uVpp), the controller 160 can issue a warning that the sense electrodemay be in poor contact or losing contact with the user's skin. (Inparticular, because amplitude of the oscillating ambient component inthe sense and reference signals may vary more widely as a function ofcapacitive coupling between the user and electrical components and powerlines in the user's vicinity, the controller 160 can implement a widertolerance for detecting proper and improper sense electrode contact frompeak-to-peak voltage component oscillating at the ambient frequency inthe composite digital sense signal.) Similarly, if the controller 160determines that the component in the composite digital sense signaloscillating at the ambient frequency exhibits a peak-to-peak voltagegreater than the high threshold ambient voltage, the controller 160 canflag the sense channel, issue a prompt to correct the sense electrode,and/or discard the composite digital sense signal for this samplingperiod.

The controller 160 can then selectively serve a warning or an electrodeadjustment prompt to the EEG test administrator overseeing the EEG testin Block S140 based on contact quality between the sense electrode andthe user's skin. The controller 160 can also selectively flag, annotate,and/or disable recordation of the composite digital sense signal readfrom this sense electrode based on such contact quality, as describedbelow.

10. Setup

In one variation, the controller 160 (and/or the native EEG testapplication executing on the external device) implements the foregoingmethods and techniques to indicate to the EEG test administrator (or tothe user) the contact state of each electrode substantially in real-timeas the EEG headset 102 is placed on the user's head and adjusted inpreparation for an EEG test. In this variation, the controller 160 canthus provide electrode contact feedback to the EEG test administratorsubstantially in real-time to enable the EEG test administrator toachieve proper contact between the user's skin and all electrodes in theEEG headset 102 before beginning the EEG test and moving physically awayfrom the user, such as to prepare another user for another EEG test witha similar EEG headset 102.

In this variation, prior to installation of the EEG headset 102 on theuser's head the controller 160 (or the native EEG test application, or aremote computer system) can also predict adjustments for the supportstructure (e.g., each headband) in the EEG in order to achieve properskin contact across each electrode. For example, during setup, the EEGtest administrator can enter the user's head shape and head side intothe native EEG test application, such as through dropdown menusenumerating qualitative head shapes (e.g., square, round, diamond,triangular, oblong, and oval) and qualitative head sizes (small, medium,and large). The native EEG test application can then retrieve predefinedsetup instructions corresponding to the combination of head shape andhead size entered by the EEG test administrator, such as a length oradjustment position of each headband within the EEG headset 102 toaccommodate the user's head shape and size. The native EEG testapplication can then serve these instructions to the EEG testadministrator through a display integrated into the device executing thenative EEG test application.

In the foregoing example, during setup, the EEG test administrator canalso enter the user's hair type, quality, and quantity into the nativeEEG test application, such as through dropdown menus enumeratingqualitative hair types (e.g., none, straight, wavy, curly, kinky, anddreadlocks) qualitative hair thicknesses (e.g., thin, full, and thick);and qualitative hair quantity (none, bald above crown, buzz, short,moderate, or long). The native EEG test application can then retrievepredefined contact insert types for each electrode based on the user'shair type, quality, and quantity entered by the EEG test administrator,such as a callout for one of: an elastic bristle insert; a rigid pronginsert; a flat contact disk insert; and a domed contact disk insert;etc. for each electrode. The native EEG test application can then servethese contact insert type callouts to the EEG test administrator throughthe device executing the native EEG test application.

Once the EEG headset 102 is placed on the user's head and adjusted toachieve proper skin contact across all electrodes in the EEG headset102, as confirmed by the controller 160 in Blocks S126 and S136, thecontroller 160 (or the native EEG test application, or a remote computersystem) can store headband adjustments and/or contact insert types foreach electrode in an electronic profile for the user. For example, theremote computer system can store this configuration as a targetconfiguration for the user in the user's electronic profile. If resultsof the subsequent EEG test indicate suitable skin contact acrosselectrodes in the EEG headset 102, such as less than 5% improper contactacross all electrodes for the entire duration of the EEG test, theremote computer system can also update this configuration for the userbased on adjustments made to the EEG headset 102 or to contact inserttypes at each electrode during the EEG test to improve contact qualityat each electrode. During setup of additional EEG tests in the future,the controller 160 (or the native EEG test application, or a remotecomputer system) can serve this headset configuration to an EEG testadministrator tasked with configuring an EEG headset 102 for the userfor these future EEG tests. Furthermore, during setup of additional EEGtests in the future, the controller 160 (or the native EEG testapplication, or a remote computer system) can serve suggestions—to theEEG test administrator—for taking special care in placing certainelectrodes on the user based on poor contact quality at these electrodesduring past EEG tests.

The controller 160 (or the native EEG test application) can implementsimilar methods and techniques to update a configuration of the EEGheadset 102 for the user based on feedback provided manually by the EEGtest administrator. For example, the EEG test administrator canenter—through the native EEG test application—various feedback,including: whether an adjustment suggested by the system resolvedelectrode contact issues; and/or types, directions, and/or degrees ofadjustment made by the EEG test administrator to bring electrodes in theEEG into proper contact with the user's scalp. Based on these feedback,the native EEG test application can refine the stored EEG headsetconfiguration for the user. The native EEG test application or remotecomputer system can also develop a generic model for predicting idealconfiguration of the EEG headset for a population of users of headshape, age, hair style and length, etc. similar to that of the userbased on feedback provided by the EEG test administrator.

The controller 160, native EEG test application, and/or remote computersystem can therefore implement various learning algorithms to developsuggestions for improving contact between electrodes in the EEG headset102 and scalps of users based on feedback supplied by EEG testadministrators over time.

However, the controller 160 (or the native EEG test application, or aremote computer system) can feed data—collected during setup andexecution of an EEG test at a user—forward to setup and execution of alater EEG test in any other way in order to reduce setup time for thelater EEG test and/or to the quality of data collected during the laterEEG test.

11. Signal Annotation

As shown in FIG. 1 , one variation of the method S100 further includesBlock S150, which recites: over a period of time, writing a digitalrepresentation of the first composite sense signal to a digital file;and annotating the digital representation of the first composite sensesignal with contact states of the driven electrode 110, the referenceelectrode 120, and the first sense electrode 131 over the period oftime. Generally, in Block S150, the controller 160 can record compositesense signals read from each sense electrode 131 to a digital file andcan annotate each composite sense signal in the digital file with thecontact states or contact state changes throughout the EEG test overwhich these composite sense signals were recorded. In particular, duringoperation (e.g., during an EEG test), the controller 160 can flag orannotate each sense channel (e.g., a data stream read from the referenceelectrode 120 and unique data streams generated from raw sense signalsread from each sense electrode 131) with its contact status (e.g., acontact loss status and/or a proper contact status), such as for eachsampling period or for each change in the contact state of thecorresponding electrode.

In one implementation, the signal processor 150: reads a raw referencesignal from the reference electrode or calculates a virtual rawreference signal from one or more sense electrodes; reads raw sensesignals from sense electrodes in the EEG headset 102; and subtracts the(virtual) raw reference signal from each raw sense signal to calculatecomposite senses signals with noise removed. The controller 160 can thenrecord each composite sense signal to the digital file (e.g., a digitalelectroencephalography test result file).

In this implementation, if the signal processor 150 determines that thereference electrode 120 or the driven electrode 110 has lost contactwith the user's skin during a particular period of time during an EEGtest in Block S122 or S124, the controller 160 can annotate a datastream read from each sense electrode 131 with a “discard” label, asthese data streams are unreliable during this particular period due tolack of proper skin contact at the drive and reference electrode. Inanother example, in Block S132, if the signal processor 150 determinesthat 18 of 19 sense electrodes are in proper contact with the user'sskin but that a 19^(th) sense electrode 131 has lost contact with theuser's skin during a particular period of time during the EEG test, thecontroller 160 can annotate a data stream from the 19^(th) senseelectrode 131 with a “contact lost” label to indicate that these data inthe 19^(th) data stream are unreliable during this particular period.

Alternatively, in Block S150 the controller 160 can stream these datastreams to a remote computer system, such as to the EEG testadministrator's smartphone over wireless communication protocol, to adesktop computer connected to the EEG headset 102, or to a remotecomputer system (e.g., a remote server) over the Internet. The EEG testadministrator's smartphone, the desktop computer connected to the EEGheadset 102, or the remote computer system can then implement similarmethods and techniques to store these data streams in a digital file andto associate these data streams with contact qualities of theircorresponding electrodes.

12. Dynamic Drive Signal

As shown in FIG. 1 , one variation of the method S100 includes:outputting a drive signal through a driven electrode 110 in Block S110,the drive signal including an alternating-current component oscillatingat a reference frequency and a direct-current component; reading areference signal from a reference electrode 120 in Block S120; inresponse to the raw reference signal including a first signal componentoscillating at the reference frequency, confirming proper contactbetween the user's skin and the driven electrode 110 and between theuser's skin and the reference electrode 120 in Block S126; reading asense signal from each sense electrode 131 in a set of sense electrodesin Block S130; in response to each sense signal read from a first subsetof sense electrodes in the set of sense electrodes at a first timeincluding a third signal component oscillating at the referencefrequency, confirming proper contact between the user's skin and thesense electrode 131 in Block S136. In this variation, the method S100further includes: for each sense electrode 131 in the first subset ofsense electrodes, calculating a composite sense signal by subtractingthe raw reference signal from the analog sense signal output by thesense electrode 131 at the first time in Block S161; calculating a firstcombination of the first set of composite signals in Block S162;compiling (e.g., combining, summing) the first combination and adirect-current component of the drive signal at approximately the firsttime to calculate a second direct-current value for the drive signal inBlock S163; and at a second time succeeding the first time, shifting thedrive signal to the second direct-current value in Block S160.

In this variation, the method S100 can similarly include: outputting adrive signal through a driven electrode, the drive signal including analternating-current component oscillating at a reference frequency and adirect-current component in Block S110; reading a set of sense signalsfrom a set of sense electrodes at a first time in Block S120;calculating a first combination of the set of sense signals in BlockS162; calculating a second direct-current value including a combination(e.g., a sum, an average, etc.) of the first combination and thedirect-current component of the drive signal at approximately the firsttime in Block S163; and at a second time succeeding the first time,shifting the direct-current component of the drive signal output by thedriven electrode to the second direct-current value in Block S160.

Generally, in Blocks S161, S162, S163, and S160, the controller 160calculates a new DC component of the drive signal based on a combinationof (raw or composite) sense signals read from each sense electrode 131that is confirmed to be in proper contact with the user's skin duringthe current sampling period and then shifts the output voltage of thedriven electrode to this new DC component during the next samplingperiod, thereby maintaining the center voltage of the drive signal at acenter of the dynamic range of the system during the next samplingperiod, such as to compensate for the output voltage of a battery 170 orother power supply integrated into the EEG headset 102. The controller160 can repeat this process throughout an EEG test, such as during eachsampling period or during each time interval (e.g., one-secondintervals) during the EEG test. In particular, the output voltage of thebattery 170 (or other power supply) supplying power to the controller160, the signal processor 150, and electrodes within the EEG headset 102may dictate a dynamic range of the signal processor 150 (e.g., thedynamic range of the ADC). Furthermore, because the output voltage ofthe battery 170 may change as the battery 170 is discharged, as thetemperature of the battery 170 changes, as the battery 170 ages, or as aload on the battery 170 changes, etc. over time, the dynamic range ofthe signal processor 150 may also change over time. Therefore, to ensurethat raw reference and sense signals read by the signal processor 150remain substantially centered within the dynamic range of the ADC overtime, the controller 160 can recalculate the DC component of the drivesignal over time. The signal generator 140 then modifies the drivesignal dynamically during an EEG test according to the new DC componentcalculated by the controller 160. The controller 160 and the signalgenerator 140 can repeat this process at or after each sampling periodduring operation of the EEG headset 102.

In one implementation, at startup (e.g., at the beginning of an EEGtest), the signal generator 140 generates a drive signal that includes aDC component at a voltage half of the nominal battery voltage. In oneexample in which the EEG headset 102 includes a battery configured tooutput a nominal 3.3V to the signal processor 150 and to amplifiers ateach reference and sense electrode 131, at startup, the signal generator140 can output a drive signal containing a 1.65V DC component to thedriven electrode 110. For each subsequent sampling period, thecontroller 160 can: calculate a combination (e.g., a linear combination,an average) of composite digital sense signals read by the signalprocessor 150 (from which the raw reference signal read from thereference electrode 120 has already been subtracted in Block S131, asdescribed above); transform the combination into a composite voltagevalue; and then combine this composite voltage value and the voltage ofthe DC component of the drive signal output during the current (orpreceding) sampling period to calculate a new DC voltage for the drivesignal at the next sampling period. The controller 160 can pass each newDC voltage of the drive signal to the signal generator 140, and thesignal generator 140 can shift the drive signal to this new DC voltageduring the next sampling period. The controller 160 can repeat thisprocess to calculate a new DC voltage of the drive signal—approximatelycentered within the dynamic range of the system, as dictated by thenominal voltage of the battery 170—for each subsequent sampling periodduring operation of the EEG headset 102.

In the foregoing implementation, because signals read from senseelectrodes determined to be in improper contact with the user's skin maybe unreliable, the controller 160 can calculate the combination ofcomposite digital sense signals originating exclusively from senseelectrodes determined to be in proper contact with the user's skinduring a current (or last) sampling period. The combination of thesecomposite digital sense signals can thus represent the combined (e.g.,average) voltage across sense electrodes in proper contact with theuser's skin during the current (or last) sampling period, less thevoltage of the reference signal during the current (or last) samplingperiod. By then combining (e.g., summing) a DC voltage represented bythe combination with the DC voltage of the drive signal during thecurrent (or last) sampling period, the controller 160 can calculate anew DC voltage—approximately aligned with the center voltage of theADC—for the drive signal. The signal generator 140 can then shift thedrive signal to this new DC voltage during the next sampling period inBlock S160.

The controller 160 can repeat this process for each sampling period (orfollowing a set of sampling periods). In particular, the controller 160can track changes in skin contact quality at each electrode anddynamically adjust a subset of composite digital sense signals combinedto calculate a composite (e.g., average) digital voltage valueaccordingly for each subsequent sampling period. For example, in BlockS160, after updating the DC component of the drive signal at a firsttime, the controller 160 can determine improper contact between theuser's skin and sense electrodes in a second subset of sense electrodesin Block S132 in response to each raw sense signal read from a secondsubset of sense electrodes in the set of sense electrodes at the firsttime excluding the third signal component oscillating at the referencefrequency (or in response to each composite sense signal read from asecond subset of sense electrodes in the set of sense electrodes at thefirst time including the third signal component oscillating at thereference frequency), wherein the second subset of sense electrodes isdistinct from the first subset of sense electrodes.

In Block S160, the controller 160 can then: identify a second subset ofsense electrodes in the set of sense electrodes in proper contact withthe user's skin at the second time, the second subset of senseelectrodes different from the first subset of sense electrodes; for eachsense electrode 131 in the second subset of sense electrodes, calculatea voltage difference, in a second set of voltage differences, between avoltage of the raw reference signal and a voltage of a sense signaloutput by the sense electrode 131 at the second time; calculate a secondcombination of the second set of voltage differences; combine (e.g.,sum, average) the second combination and a voltage of the direct-currentcomponent of the drive signal at approximately the second time tocalculate a third direct-current voltage of the drive signal; and at athird time succeeding the second time, shift the direct-currentcomponent of the drive signal to the third direct-current voltage.

In particular, the signal processor 150 can continuously sample thesense electrodes. During each scan cycle, the controller can define asubset of sense electrodes in proper contact with the user's skin andthen flag (raw or composite) sense signals read from each senseelectrode in this subset of sense electrodes for calculation of the DCcomponent of the drive signal output by the driven electrode in the nextscan cycle.

Furthermore, when the driven electrode 110 and/or the referenceelectrode 120 are determined to have lost contact with the user's skin,the controller 160 can maintain a last DC component of the drive signalunchanged. In particular, in response to determination of impropercontact between the user's skin and one of the driven electrode 110 andthe reference electrode 120, the controller 160 can maintain thedirect-current component of the drive signal substantially unchangeduntil proper contact between the user's skin and the driven electrode110 and between the user's skin and the reference electrode 120 areconfirmed.

Alternatively, in this variation, for the signal processor 150 thatexhibits a dynamic range less than the nominal voltage output of thebattery 170, at startup, the signal generator 140 can generate a drivesignal that includes a DC component at a voltage (above the batteryground) half of the dynamic range of the signal processor 150. Thecontroller 160 can then implement averaging techniques as describedabove to calculate a new drive signal DC voltage that centers theaverage outputs of the sense electrodes (and the reference electrode120) for the current (or last) sampling period within the dynamic rangeof the signal processor 150.

For example, the controller 160 can: calculate a combination ofcomposite digital sense signals read (from sense electrodes determinedto be in proper contact with the user's skin) by the signal processor150; combine (e.g., sum) this combination and a digital valuerepresenting the voltage of the DC component of the drive signal outputduring the current (or preceding) sampling period to calculate acomposite (e.g., average) digital center signal value for the currentsampling period. The controller 160 can then: calculate a digitaldifference by subtracting this composite digital center signal from thecenter of the dynamic range of the signal processor 150 (e.g., “127” foran 8-bit ADC outputting digital values between 0 and 255 in each sensechannel); transform this digital difference value into a voltagedifference; and add this voltage difference to the current (or last) DCvoltage of the drive signal to calculate a new DC voltage for the drivesignal at the next sampling period. The signal generator 140 can thenimplement this DC voltage accordingly at the next sampling period, asdescribed above.

The signal generator 140 can therefore output a drive signal including aDC component that follows the sense signals (and the raw referencesignal) collected by the sense electrodes (and by the referenceelectrode 120). The signal generator 140 can combine the dynamic DCcomponent with a static AC component, such as a sinusoidal, 2.0 Hz, 17millivolt peak-to-peak AC signal, as described above. However, thesignal generator 140 can output a drive signal including DC and ACcomponents at any other voltage and—for the AC component—oscillating atany other frequency and according to any other waveform. Furthermore,the controller 160 can implement the foregoing methods and techniques toprocess raw or composite analog sense signals to calculate a new DCcomponent of the drive signal for each subsequent scan cycle.

12. Motion Tracking

In one variation, the EEG headset 102 further includes an accelerometer,gyroscope, compass, and/or other motion sensor, such as arranged in thehousing described above. In this variation, the controller 160 cansample the motion sensor during operation (e.g., during an EEG test),correlate an output of the sensor with a magnitude and/or direction ofmotion of the user's head, and set an excess motion flag in response tothe magnitude of motion of the user's head exceeding a threshold motion(e.g., acceleration) magnitude. The wireless communication module 162can then push an excess motion notification to the external devicesubstantially in real-time based on the excess motion flag. For example,the controller 160 can generate a notification including a textualprompt to quell the user, such as reciting, “The user is exceeding amotion limit for the current EEG test,” and the wireless communicationmodule 162 can push this notification to the external device, asdescribed above, for substantially immediate response by the EEG testadministrator. Based on the notification, the EEG test administrator canthen return to and quiet the user.

Generally, movements by the user during the EEG test may createartifacts in the EEG data collected during the EEG test and/or may causean electrode to lose contact with the user's skin. The EEG headset 102can therefore sample the motion sensor during the EEG test, characterizethe outputs of the motion sensor, and notify an EEG test administratorif the user's motion exceeds a motion limit, such as a motion limitcharacterized by relatively high risk of data artifacts or by relativelyhigh risk of loss of electrode contact. The EEG headset 102 cantherefore provide guidance to the EEG test administrator—through theexternal device or through an audible or visual indicator on the EEGheadset 102—to minimize user motion that may create artifacts in EEGtest data or lead to low-quality EEG data collected during the EEG test.

In one implementation, the EEG headset 102 includes an accelerometer,and the controller 160 retrieves acceleration limits for various motiontypes specified for an upcoming EEG test and generates excess motionnotifications while the EEG test is in process based on these specifiedacceleration limits. For example, the controller 160 can access adatabase in which a maximum (X-, Y-, and Z-axis) composite accelerationfor each of multiple motion types are specified for available EEG tests,including a walking-type motion characterized by accelerations below 0.5Hz, a fidgeting motion characterized by accelerations between 0.5 Hz and1.0 Hz, a talking-type motion characterized by accelerations between 1.0Hz and 2.0 Hz, and a blinking-type motion characterized by accelerationsgreater than 2.0 Hz, etc. In this example, the database can definemoderate acceleration limits for the walking-, fidgeting-, talking-, andblinking-type motions for a general seated EEG test, whereas thedatabase can define relatively low acceleration limits for blinking-typemotions for frontal lobe tests and relatively high acceleration limitsfor temporal lobe tests. Furthermore, in this example, for a generalwalking EEG test, the database can define a relatively high accelerationlimit for walking-type motions and a relatively low acceleration limitfor talking-type motions. The EEG headset 102 can therefore compareacceleration values output by the accelerometer to EEG test-specificmotion limits to identify instances of excess motion, and the EEGheadset 102 can generate and distribute notifications to the EEG testadministrator (or directly to the user) accordingly.

Alternatively, the EEG headset 102 can implement generic motion limitsacross all EEG tests and can selectively activate and deactivate flagsfor excess motion types based on a type of the current EEG test. Forexample, when a general walking EEG test is underway, the EEG headset102 can deactivate motion limits for walking-type and fidgeting-typemotions but maintain motion limits for talking-type and blinking-typemotions. However, in this example, when a seated frontal lobe test isunderway, the EEG headset 102 can activate motion limits for allwalking-, fidgeting-, talking-, and blinking-type motions.

The EEG headset 102 can additionally or alternatively notify the userdirectly of excess motion (and/or of electrode contact loss events, asdescribed above), such as through a speaker integrated into the EEGheadset 102 or through an external device (e.g., a smartphone, a tablet)carried or accessible directly by the user. However, the EEG headset 102can implement any other method or technique to notify the EEG testadministrator and/or the user of excess user motion and of electrodecontact loss events. The EEG headset 102 can also annotate EEG datacollected during the EEG test with motion data recorded through themotion sensor during the EEG test, such as by noting periods in eachsense channel that corresponds in time to periods of over-activity orexcessive motion by the user.

14. Active and Inactive Electrode Sets

One variation of the method shown in FIGS. 2C and 7 includes Block S170,which recites selectively activating a first subset of sense electrodesin the EEG headset 102. In this variation, the EEG headset 102 canrecord sense signals from this first subset of sense electrodes to thedigital file in Block S150 in order to limit file size and/or requiredbandwidth to transmit the digital file to another device without losingrelevant or requested data. The EEG headset 102 can also track the DCcomponent of the drive signal to a combination of sense signals readfrom the first subset of sense electrodes in Block S160 in order tocenter these sense signals within the dynamic range of these senseelectrodes, thereby maintaining relatively high fidelity and limited“clipping” in these signals of interest. Furthermore, in this variation,the EEG headset 102 can selectively activate a second subset of senseelectrodes—distinct from or overlapping the first subset of senseelectrodes—and calculate a virtual reference signal from sense signalsread from this second subset of sense electrodes in Block S121 in orderto isolate the reference signal from signals of interest across theuser's scalp, thereby maintaining high selectively to rejection of noisein composite sense signals written to the digital file in Block S150.

Therefore, in Block S170, the EEG headset 102 can execute Blocks of themethod to selectively activate and deactivate sense electrodes, toselectively record sense signals corresponding to channels of interest,to selectively calculate virtual reference signals from multiple sensesignals that may or may not correspond to channels of interest, and todynamically adjust the DC component of the drive signal to follow sensesignals corresponding to channels of interest, thereby rejecting noisein recorded signals while also limiting rejection of signalsrepresentative of local brain activity of interest.

Furthermore, by setting select sense electrodes as inactive during anEEG test, the controller 160 can: decrease power consumption therebyextending battery life of the EEG headset 102; and reduce measurementnoise, such as less digital noise and power noise, thereby yieldinghigher-quality data for the channels of interests.

14.1 Active Electrode Selection

In one implementation, the native EEG test application—executing on theexternal device that is paired with the EEG headset 102—contains a listof selectable, preconfigured EEG test types, wherein each EEG test typespecifies a test duration and defines a set of active sense electrodescorresponding to channels of interest (or located over an area ofinterest of a user's skull by EEG headset 102), as shown in FIG. 7 . Inthis example, the native EEG test application can store a set ofpreconfigured EEG test types and parameters, including: a full EEG testtype specifying a 40-minute duration with all 19 sense electrodes active(i.e., relevant to the full EEG test); a frontal lobe test typespecifying a 20-minute duration with sense electrodes at the fivefrontal lobe positions (e.g., FZ, F3, F7, F4, and F8) and the twofrontal polar sites (e.g., Fp1 and Fp2) active and all other senseelectrodes inactive or allocated for calculation of a virtual referencesignal; and a right-temporal lobe test type specifying a 15-minuteduration and the two right-temporal lobe sense electrodes (e.g., T4 andT6) active and all other sense electrodes inactive; etc.

In another implementation, the native EEG test application canadditionally or alternatively enable an EEG test administrator (or aneurologist, etc.) to design or configure a custom EEG test, such as acustom EEG test specifying a custom duration and a custom subset ofoccipital lobe, frontal lobe, parietal lobe, and/or center positionsense electrodes as active, as shown in FIG. 7 . Furthermore, the nativeEEG test application can enable the EEG test administrator (or aneurologist, etc.) to design or manually configure a dynamic EEG test inwhich a subset of active sense electrodes changes throughout theduration of the custom EEG test, such as based on time from start of theEEG test or based on artifacts or neural oscillations recorded duringthe EEG test.

Furthermore, through the native EEG test application, the EEG testadministrator can select a standard EEG test from a pre-populated listof EEG tests, modify an existing EEG test, or configure a custom EEGtest for an upcoming EEG test period. The external device executing thenative EEG test application can then upload parameters of the selectedor (re)configured EEG test to the EEG headset 102—such as in the form ofidentifiers or addresses of active sense electrodes and active timedurations for each sense electrode)—such as over short-range wirelesscommunication protocol in preparation for execution of a new EEG test bythe EEG headset 102.

Upon selection of a set of channels of interest (or an area of intereston a user's scalp), the signal processor 150 can classify each senseelectrode in the EEG headset 102 as one of: inactive (e.g., off andelectrically isolated from the ADC); active and of interest (e.g., foroutputting a sense signal that is recorded to a digital file and that isused to adjust the DC component of the drive signal); and active forvirtual reference signal calculation (e.g., for outputting a sensesignal exclusively for calculating a virtual reference). In particular,the signal processor 150 can label each sense electrode corresponding toa channel of interest as active and of interest and define a firstsubset of these sense electrodes. As described above, the signalprocessor 150 can also label a second subset of sense electrodes asactive for virtual reference signal calculation, such as based on apredefined second subset of sense electrodes for the selected EEG testtype or based on a set of rules for selecting the second subset of senseelectrodes based on the first subset of sense electrodes. The signalprocessor 150 can then label all other sense electrodes as inactive.

By labeling each sense electrode and allocating each sense electrode toa particular “bucket,” the signal processor 150 can prepare to: recordsense signals from areas or channels of interest exclusively; maintainsense signals of interest with the dynamic range of sense electrodes inthe first subset by tracking the DC component of the drive signal to theaverage center voltage of these sense signals of interest; and tocalculate a virtual reference signal from other targeted senseelectrodes in contact with the user's skin during the subsequent EEGtest. The signal processor can also selectively deactivate senseelectrodes and the controller 160 can selectively issue electrodeadjustment prompts based on labels assigned to each sense electrode, asdescribed below.

14.2 Dynamic Active Electrode Selection

In this variation, the signal processor 150 can also dynamically adjustthe first and second subsets of sense electrodes throughout an EEG test.For example, the native EEG test application can enable the EEG testadministrator to select and order multiple EEG test types into onecomposite EEG test and to then upload this composite EEG test to the EEGheadset 102 for execution during a single session (i.e., one contiguousduration of time in which the EEG headset 102 is worn by one user). TheEEG headset 102 can then implement methods and techniques describedabove to dynamically adjust the first and second subsets of senseelectrodes as one EEG test is completed and a next EEG test is begunwithin the test session.

In the foregoing example, the EEG headset can: receive selection of afirst EEG test specifying a first set of channels of interest and afirst duration; and receive selection of a second EEG test specifying asecond set of channels of interest and a second duration, wherein thesecond set of channels of interest differs from the first set ofchannels of interest. During execution of the first EEG test, the EEGheadset 102 can: populate a first subset of sense electrodescorresponding to the first set of channels of interest; populate asecond subset of sense electrodes matched to the first subset of senseelectrodes; sample the first and second subsets of sense electrodes, asdescribed above; and write the first set of sense signals to a firstdigital electroencephalography test result file corresponding to thefirst electroencephalography test over the first duration within a testperiod. The EEG headset 102 can also: select a third subset of senseelectrodes corresponding to the second set of channels of interest;select a fourth subset of sense electrodes matched to the third set ofsense electrodes; transition to reading sense signals from the third andfourth subsets of sense electrodes upon conclusion of the first durationwithin the test period; and write a third set of sense signals to adigital electroencephalography test result file corresponding to thesecond electroencephalography test over the second duration within thetest period.

However, the EEG headset 102 can implement any other method or techniqueto automatically transition between preselected EEG tests within one EEGtest session.

14.2 Dynamic Drive Signal

In this variation, the EEG headset 102 can map the DC component of thedrive signal to a subset of sense electrodes, such as to the firstsubset of sense electrodes corresponding to channels of interest or anarea of interest specified in the current EEG test. For example, inresponse to determining that a sense electrode in the first subset ofsense electrodes has lost contact with the user's skin in Block S132 asdescribed above, the signal processor 150 can remove the correspondingsense signal from the combination of sense signals calculated in BlockS162 as described above. In this example, the EEG headset 102 can: reada first set of sense signals from the first subset of sense electrodes;determine improper contact between the user's skin and a first senseelectrode in the first subset of sense electrodes in response to a firstsense signal in the first set of sense signals excluding a first signalcomponent oscillating at the reference frequency in Block S130; adjustthe direct-current component of the drive signal to follow a combinationof the first subset of sense signals—excluding the first sense signal—inresponse to detecting improper contact between the user's skin and thefirst sense electrode in Block S162; and transmit a prompt to adjust thefirst sense electrode to the EEG test administrator in Block S140. Thesignal processor 150 can therefore reject the corresponding sense signalfrom calculation of the DC component of the drive signal for the nextsampling period such that the DC component of the drive signal followsthe average of sense signals read from sense electrodes confirmed to bein proper contact with the user's skin.

Alternatively, in this implementation, the signal processor 150 cancompile sense signals read from sense electrodes in both the first andsecond subsets of electrodes into a target DC value for the DC componentof the drive signal such that sense signals read from these senseelectrode—and written to a digital file and manipulated to calculate thevirtual reference signal, respectively—remain approximately centeredwithin the dynamic range of the EEG headset 102.

14.4 Notifications and Actions

In this variation, the EEG headset 102 can selectively respond tocontact loss events at sense electrodes based on labels written to thesesense electrodes before or during the EEG test.

In one implementation, when the signal processor 150 determines that afirst sense electrode in the first subset of sense electrodes (i.e.,corresponding to channels of interest for the current EEG test) has lostcontact with the user's skin in Block S132, the EEG headset 102 canautomatically remove a first sense signal—read from the first senseelectrode—from calculation of a new target DC component of the drivesignal in Blocks S161, S162, and S163. For example, in this variation,the EEG headset 102 can: receive selection of a set of channels ofinterest; select a first subset of sense electrodes—in a set of senseelectrodes integrated into an electroencephalographyheadset—corresponding to the set of channels of interest; and output adrive signal through the driven electrode during a test period. In thisexample, the EEG headset 102 can then: read a first set of sense signalsfrom the first subset of sense electrodes; calculate a first combinationof the first set of sense signals; and adjust the direct-currentcomponent of the drive signal to follow the first combination over afirst duration within the test period. Over a second duration within thetest period, the EEG headset 102 can also: read a second set of sensesignals from the first subset of sense electrodes; in response to asecond sense signal read from a first sense electrode in the firstsubset of sense electrodes excluding a first signal componentoscillating at the reference frequency, determine that the first senseelectrode is in improper contact with the user's skin; calculate asecond combination of the second set of sense signals, now excluding thesecond sense signal read from the first sense electrode; and adjust thedirect-current component of the drive signal to follow the secondcombination.

In the foregoing implementation, the EEG headset 102 can alsoimmediately broadcast a prompt to correct the first sense electrode inBlock S140 when such loss of contact is detected. Because the firstsense electrode corresponds to a channel of interest, the EEG headset102 can continue to record the first sense signal to the digital file inBlock S150 but annotate this channel, as described above. Alternatively,in order to reduce crosstalk between the first set and other activesense electrodes in the first subset or noise injection into these otherchannels due to the loss of skin contact at the first sense electrode,the EEG headset 102 can automatically deactivate the first senseelectrode upon detection of loss of contact between the first senseelectrode and the user's skin.

Similarly, when the signal processor 150 determines that a second senseelectrode in the second subset of sense electrodes (i.e., active duringthe EEG test exclusively for calculation of a virtual reference signal)has lost contact with the user's skin in Block S132, the EEG headset 102can automatically remove a second sense signal—read from the secondsense electrode—from calculation of the virtual reference signal inBlock S121. In this implementation, if more than a threshold number ofsense electrodes in the second subset remain in proper contact with theuser's skin when the second sense signal loses contact, the EEG headset102 can: automatically deactivate the second sense electrode; and/orwithhold transmission of a prompt to correct the second sense electrodeto the EEG test administrator in Block S140. If the EEG headset 102later determines that a first electrode in the first subset of senseelectrode electrodes of interest has lost contact with the user's skin,the EEG headset 102 can append a prompt to correct the second senseelectrode with a prompt to correct the first sense electrode andtransmit the composite prompts to the EEG test administrator forrectification of both the first and second sense electrodes.

However, if fewer than the threshold number of sense electrodes in thesecond subset remain in proper contact with the user's skin when thesecond sense signal loses contact, the EEG headset 102 can immediatelytransmit such a prompt to correct the second sense electrode to the EEGtest administrator in Block S140.

15. Remote Signal Processing

In one variation, the EEG headset 102 transmits electrode data (e.g.,the digital reference signal and composite digital sense signals) to theremote external device substantially in real-time, and the externaldevice implements methods and techniques described above to transformthese electrode data into electrode contact qualities and to issuenotifications—through its integrated display—to correct instances ofpoor electrode contact.

The systems and methods described herein can be embodied and/orimplemented at least in part as a machine configured to receive acomputer-readable medium storing computer-readable instructions. Theinstructions can be executed by computer-executable componentsintegrated with the application, applet, host, server, network, website,communication service, communication interface,hardware/firmware/software elements of a user computer or mobile device,wristband, smartphone, or any suitable combination thereof. Othersystems and methods of the embodiment can be embodied and/or implementedat least in part as a machine configured to receive a computer-readablemedium storing computer-readable instructions. The instructions can beexecuted by computer-executable components integrated bycomputer-executable components integrated with apparatuses and networksof the type described above. The computer-readable medium can be storedon any suitable computer readable media such as RAMs, ROMs, flashmemory, EEPROMs, optical devices (CD or DVD), hard drives, floppydrives, or any suitable device. The computer-executable component can bea processor, but any suitable dedicated hardware device can(alternatively or additionally) execute the instructions.

As a person skilled in the art will recognize from the previous detaileddescription and from the figures and claims, modifications and changescan be made to the embodiments of the invention without departing fromthe scope of this invention as defined in the following claims.

I claim:
 1. A method comprising: receiving selection of a set ofchannels of interest; selecting a first subset of sense electrodes, in aset of sense electrodes integrated into an electroencephalographyheadset, corresponding to the set of channels of interest; selecting asecond subset of sense electrodes, in the set of sense electrodes,differing from the first subset of sense electrodes; during a testperiod, outputting a drive signal through a driven electrode integratedinto the electroencephalography headset, the drive signal comprising analternating-current component oscillating at a reference frequency and adirect-current component; over a first duration of a test period:reading a first set of sense signals from the first subset of senseelectrodes; reading a second set of sense signals from the second subsetof sense electrodes; adjusting the direct-current component of the drivesignal to follow a first linear combination of the first subset of sensesignals; calculating a virtual reference signal as a function of thesecond set of sense signals; and recording differences between the firstset of sense signals and the virtual reference signal.
 2. The method ofclaim 1: wherein receiving selection of the set of channels of interestcomprises receiving selection of an electroencephalography testspecifying the set of channels of interest; and wherein selecting thesecond subset of sense electrodes comprises selecting the second subsetof sense electrodes distinct from and remotely located from the firstsubset of electrodes on the electroencephalography headset.
 3. Themethod of claim 1, further comprising, over a second duration of thetest period succeeding the first duration: reading a third set of sensesignals from the first subset of sense electrodes; detecting abnormalcontact between the user's skin and a first sense electrode in the firstsubset of sense electrodes in response to a third sense signal in thethird set of sense signals excluding a first signal componentoscillating at the reference frequency; and in response to detectingabnormal contact between the user's skin and the first sense electrode:adjusting the direct-current component of the drive signal to follow asecond linear combination of the third subset of sense signals less thethird sense signal; and generating an electronic notification comprisinga prompt to adjust the first sense electrode.
 4. The method of claim 1,further comprising, over a second duration of the test period succeedingthe first duration: reading a fourth set of sense signals from thesecond subset of sense electrodes; detecting abnormal contact betweenthe user's skin and a second sense electrode in the second subset ofsense electrodes in response to a fourth sense signal in the second setof sense signals excluding a first signal component oscillating at thereference frequency; and in response to detecting abnormal contactbetween the user's skin and the second sense electrode: deactivating thesecond sense electrode; and calculating a second virtual referencesignal as a function of the second set of sense signals less the fourthsense signal; and recording differences between the first set of sensesignals and the second virtual reference signal.
 5. The method of claim4, further comprising, in response to detecting abnormal contact betweenthe user's skin and a proportion of sense electrodes, in the secondsubset of sense electrode, exceeding a threshold proportion: generatingan electronic notification comprising a prompt to adjust the senseelectrodes in the second subset of sense electrodes; and transmittingthe electronic notification to an external computing device accessibleby a biosignal test administrator.
 6. A method comprising: receivingselection of a set of channels of interest; selecting a first subset ofsense electrodes, in a set of sense electrodes integrated into anelectroencephalography headset, corresponding to the set of channels ofinterest; selecting a second subset of sense electrodes, in the set ofsense electrodes, differing from the first subset of sense electrodes;during a test period beginning at a first time: outputting a drivesignal through a driven electrode integrated into theelectroencephalography headset worn by a user, the drive signalcomprising an alternating-current component oscillating at a referencefrequency and a direct-current component; reading a first set of sensesignals from the first subset of sense electrodes; reading a second setof sense signals from the second subset of sense electrodes; in responseto a second sense signal read from a second sense electrode in thesecond subset of sense electrodes excluding a first signal componentoscillating at the reference frequency at a second time succeeding thefirst time, detecting that the second electrode is in abnormal contactwith the user's skin; and in response to detecting that the secondelectrode is in abnormal contact with the user's skin, deactivating thesecond electrode.
 7. The method of claim 6, further comprising: from thefirst time to the second time, calculating a first virtual referencesignal as a function of the second set of sense signals read from thesecond subset of sense electrodes; following the second time,calculating a second virtual reference signal as a function of thesecond set of sense signals read from the second subset of senseelectrodes less the second sense electrode; and during the test period,calculating a first composite sense signal by subtracting the referencesignal from a first sense signal read by a first sense electrode in thefirst subset of sense electrode; and storing the first composite sensesignal in a digital electroencephalography test result file.
 8. Themethod of claim 7, further comprising: following the third time,calculating a third virtual reference signal as a function of the secondset of sense signals read from the second subset of sense electrodesless the second sense electrode; in response to the second referencesignal excluding a first signal component oscillating at the referencefrequency and comprising a second signal component oscillating at anambient frequency: detecting that the driven electrode is in abnormalcontact with the user's skin; generating an electronic notificationcomprising a prompt to adjust the first sense electrode; andtransmitting the electronic notification to an external computing deviceaccessible by a biosignal test administrator.
 9. The method of claim 6,further comprising: in response to a first sense signal read from afirst sense electrode in the first subset of sense electrodes excludinga first signal component oscillating at the reference frequency at athird time succeeding the second time, detecting that the firstelectrode is in abnormal contact with the user's skin; in response todetecting that the first electrode is in abnormal contact with theuser's skin: generating an electronic notification comprising a promptto adjust the first sense electrode; and transmitting the electronicnotification to an external computing device accessible by a biosignaltest administrator.
 10. The method of claim 9, wherein generating theelectronic notification comprises generating the electronic notificationcomprising the prompt to adjust the first sense electrode and the senseelectrode.
 11. The method of claim 6, further comprising, at a thirdtime succeeding the second time by a check duration: reactivating thesecond sense electrode; reading a third sense signal from the secondsense electrode; in response to the third sense signal comprising thefirst signal component oscillating at the reference frequency, detectingthat the second electrode is in proper contact with the user's skin atthe third time; and in response to detecting that the second electrodeis in proper contact with the user's skin, maintaining the secondelectrode in an active state following the third time.
 12. The method ofclaim 6: wherein receiving selection of the set of channels of interestcomprises receiving selection of the set of channels of interest for afirst electroencephalography test of a first duration; furthercomprising receiving selection of a second set of channels of interestfor a second electroencephalography test of a second duration, thesecond set of channels of interest different from the first set ofchannels of interest; selecting a third subset of sense electrodes, inthe set of sense electrodes, corresponding to the second set of channelsof interest; selecting a fourth subset of sense electrodes, in the setof sense electrodes, differing from the third subset of senseelectrodes; over the first duration within the test period, writing thefirst set of sense signals to a first digital electroencephalographytest result file corresponding to the first electroencephalography test;in response to conclusion of the first duration within the test period,transitioning to reading a third set of sense signals from the thirdsubset of sense electrodes; and over the second duration within the testperiod succeeding the first duration, writing the third set of sensesignals to a digital electroencephalography test result filecorresponding to the second electroencephalography test.
 13. The methodof claim 6, further comprising, at approximately the first time:calculating a first linear combination of the first set of sensesignals; calculating a first direct-current value comprising a sum ofthe first linear combination and the direct-current component of thedrive signal; and shifting the direct-current component of the drivesignal output by the driven electrode to the first direct-current value.14. The method of claim 13: wherein calculating the first linearcombination comprises calculating the first linear combination of thefirst set of sense signals and the second set of sense signals atapproximately the first time; further comprising, at approximately thesecond time: calculating a second linear combination of the first set ofsense signals and the second set of sense signals less the second sensesignal; calculating a second direct-current value comprising a sum ofthe sense linear combination and the direct-current component of thedrive signal; and shifting the direct-current component of the drivesignal output by the driven electrode to the second direct-currentvalue.
 15. The method of claim 13, further comprising: in response to afirst sense signal read from a first sense electrode in the first subsetof sense electrodes excluding a first signal component oscillating atthe reference frequency at a third time succeeding the second time,detecting that the first electrode is in abnormal contact with theuser's skin; at approximately the third time: calculating a third linearcombination of the first set of sense signals less the first sensesignal; calculating a third direct-current value comprising a sum of thethird linear combination and the direct-current component of the drivesignal; and shifting the direct-current component of the drive signaloutput by the driven electrode to the third direct-current value. 16.The method of claim 6: wherein receiving the selection of the set ofchannels of interest comprises receiving manual selection of the set ofchannels of interest, in a set of channels supported by theelectroencephalography headset, during the test period; and furthercomprising, in response to receipt of manual selection of the set ofchannels of interest, activating each sense electrode in the firstsubset of sense electrodes.
 17. A method comprising: receiving selectionof a set of channels of interest; selecting a first subset of senseelectrodes, in a set of sense electrodes integrated into anelectroencephalography headset, corresponding to the set of channels ofinterest; during a test period, outputting a drive signal through adriven electrode integrated into the electroencephalography headset wornby a user, the drive signal comprising an alternating-current componentoscillating at a reference frequency and a direct-current component;over a first duration within the test period: reading a first set ofsense signals from the first subset of sense electrodes; calculating afirst linear combination of the first set of sense signals; andadjusting the direct-current component of the drive signal to follow thefirst linear combination; over a second duration within the test period:reading a second set of sense signals from the first subset of senseelectrodes; in response to a second sense signal read from a first senseelectrode in the first subset of sense electrodes excluding a firstsignal component oscillating at the reference frequency, detecting thatthe first electrode is in abnormal contact with the user's skin;calculating a second linear combination of the second set of sensesignals less the second sense signal; and adjusting the direct-currentcomponent of the drive signal to follow the second linear combination.18. The method of claim 17, further comprising: in response to detectingof abnormal contact between the user's skin and the first senseelectrode, generating an electronic notification comprising a prompt toadjust the first sense electrode; and transmitting the electronicnotification to an external computing device accessible by a biosignaltest administrator.
 19. The method of claim 17: wherein selecting thefirst subset of sense electrodes comprises activating each senseelectrode in the first subset of sense electrodes; and furthercomprising, in response to detecting of abnormal contact between theuser's skin and the first sense electrode, deactivating the first senseelectrode.
 20. The method of claim 17, further comprising: reading areference signal from a second sense electrode in the set of senseelectrodes; over the first duration within the test period, recordingdifferences between the first set of sense signals and the referencesignal to a digital electroencephalography test result file; and overthe second duration within the test period, recording differencesbetween the second set of sense signals, less the second sense signal,and the reference signal to the digital electroencephalography testresult file.